Help with engine chirping noise

[Lattimer]

I have a 350 crate motor in my truck, about 5000 miles on it now, and I have developed an intermittent chirping noise that I can't seem to locate. Engine is a 1-piece rear main block with Vortec heads, aluminum manifold, 625 cfm 4-bbl. Manual trans, stock style clutch rod setup.


It doesn't make the noise at all until it warms up.

Then the noise will come and go. By ear, it seems to be on the left bank of the engine. In gear, in neutral, clutch in, clutch out, on brakes, off brakes, makes no difference. Chirp is definitely tied to RPM, gets faster as engine revs. Also gets louder as engine revs.

Alternator, water pump are new. PS pump recently rebuilt. Electric fans so its not a fan clutch. I have tried spraying and soaping the belts. All parts are new in the last year. Standard v-belts. Replaced the header gasket yesterday as a guess, and still nothing.

I can't seem to find it with a stethoscope, everything I touch sounds normal. I have checked the water pump, PS pump, alternator, every inch of the top end. Valve train sounds normal. Can't seem to find a vacuum leak, tried the carb spray all over and found nothing. Can't hear the chirp at all with the stethoscope.

Sometimes if I turn the truck off and restart it, the noise is gone. Other times it comes right back. Sometimes while idling at a light it will stop, then comes back when rpm's come up.

Other than the noise, the truck runs great. Starts easy, idles fine, great power, etc. No other funny noises.


Hoping somebody can offer some ideas to check! Thanks in advance!

[homemade87]

One thing you can do to eliminate the front accessories is take the belts off after it warms up and starts making the noise and start it back . If it goes away then possible a angry belt or a bearing . If no then it is definitely toward the engine side . Give it a try and let us know .

[geezer#99]

I've had fuel pump push rods do that!
And had a too long bolt on the intake touching a pushrod occasionally.

[sKnNyPpY]

My exhaust hangers chirp intermentently, real high pitched and irregular

[cadillac_al]

I would bet my $1 on the alternator. I've got a screecher that I haven't changed yet. It screeches mercilessly for a couple minutes then it quits. It probably started as a light chirping that I didn't notice.

[Lattimer]

Originally Posted by cadillac_al

I would bet my $1 on the alternator. I've got a screecher that I haven't changed yet. It screeches mercilessly for a couple minutes then it quits. It probably started as a light chirping that I didn't notice.

That was my first bet so I swapped it out early in the search.....no luck.

[68gmsee]

I have a stethoscope but I found that a 2½-3 ft. piece of firm or stiff water hose works best for isolating noises for me. I saved a cheap older hose for this reason.

It's firm enough so I can place one end on my ear and use the other end to place on the engine without my hand or face getting close to the moving or hot parts. I have found squeaks on the power steering pump, on belts, tensioner pulley, a squeaking heat riser and exhaust/vacuum leaks with it.

[Lattimer]

OK, ran it with the belts off and no change at all.


I tried the water hose also and still can't track this down. It's driving me nuts.

[homemade87]

Originally Posted by Lattimer

OK, ran it with the belts off and no change at all.


I tried the water hose also and still can't track this down. It's driving me nuts.

Ok , That rules out everything on the front of the engine . Are you sure there is no exhaust leak . The noise is temperature sensitive and it wont take much to create a noise like that . An exhaust leak ( squeak ) will not be detectable with a hose or stethoscope . If you are not hearing anything on the valve covers I would suspect the exhaust . Take a closer look and let us know .

[Lattimer]

Originally Posted by homemade87

Ok , That rules out everything on the front of the engine . Are you sure there is no exhaust leak . The noise is temperature sensitive and it wont take much to create a noise like that . An exhaust leak ( squeak ) will not be detectable with a hose or stethoscope . If you are not hearing anything on the valve covers I would suspect the exhaust . Take a closer look and let us know .

Thats why I changed the header gasket last weekend. It was my last stab at what I thought it could be.
It was leaking a little on the back cylinder, you could see the black mark on the header side of the gasket once it was apart.

I went through today and retorqued the bolts now that is has a couple heat cycles on it. Just for fun I retorqued the carb base bolts and the other header as well.

Collector gaskets are new also.

Noise is definitely louder on the driver's side of the engine bay.

[68gmsee]

Maybe a short video clip would help in case others have heard similar sound. In my experience noises are the hardest things to isolate. Especially if you've never heard it before.

I've worked on machinery all my life and one of the ways I isolate an unusual noise is to watch the movement of parts to see if they coincide with the sound -a rotating pulley or even a vibrating part. Try manually revving the engine from the carb. Do it slow and then quickly to see if anything changes. Squirt spray lube on all rubber mounts, hinges, etc. I did that to isolate a squeak in my front end once.

[homemade87]

Have you stuck your head under the truck to see if it is louder or quieter . I see you say headers , is it headers or a cast manifold . If cast it may have a crack in it . Also some of the cheaper headers don't have the 3/8" thick flange and don't seal very well .

Ok , lets try another approach . I still think it is exhaust . If the drivers side is where it is loudest .Instead of tightening the header bolts when it starts to squeak try loosening all the header bolts on the drivers side . You will get some exhaust noise but we are trying to stop the squeak . If no more squeak then it is that header . Just be careful and don't get burnt . You mat just loosen them before you start it . Just trying to eliminate the headers . If the squeak is still present you should still be able to still hear it .

Heres my way of thinking . A squeak can be created if pressure is pushed out a small narrow opening. By loosening the header bolts that opening will get bigger and the squeak should stop. At this point its worth a try .

Let us know how it goes .

[4x4toy]

Are you running a PCV valve? If so pull it out of valve cover to see if noise goes away. If goes away check for broken or wrong valve. Had engine with faulty valve pull too much vacuum on crankcase and front and rear seals would chirp/squeak.

[Lattimer]

Originally Posted by homemade87

Have you stuck your head under the truck to see if it is louder or quieter . I see you say headers , is it headers or a cast manifold . If cast it may have a crack in it . Also some of the cheaper headers don't have the 3/8" thick flange and don't seal very well .

Ok , lets try another approach . I still think it is exhaust . If the drivers side is where it is loudest .Instead of tightening the header bolts when it starts to squeak try loosening all the header bolts on the drivers side . You will get some exhaust noise but we are trying to stop the squeak . If no more squeak then it is that header . Just be careful and don't get burnt . You mat just loosen them before you start it . Just trying to eliminate the headers . If the squeak is still present you should still be able to still hear it .

Heres my way of thinking . A squeak can be created if pressure is pushed out a small narrow opening. By loosening the header bolts that opening will get bigger and the squeak should stop. At this point its worth a try .

Let us know how it goes .

I'll give that a shot.

[Lattimer]

Originally Posted by homemade87

Have you stuck your head under the truck to see if it is louder or quieter . I see you say headers , is it headers or a cast manifold . If cast it may have a crack in it . Also some of the cheaper headers don't have the 3/8" thick flange and don't seal very well .

Ok , lets try another approach . I still think it is exhaust . If the drivers side is where it is loudest .Instead of tightening the header bolts when it starts to squeak try loosening all the header bolts on the drivers side . You will get some exhaust noise but we are trying to stop the squeak . If no more squeak then it is that header . Just be careful and don't get burnt . You mat just loosen them before you start it . Just trying to eliminate the headers . If the squeak is still present you should still be able to still hear it .

Heres my way of thinking . A squeak can be created if pressure is pushed out a small narrow opening. By loosening the header bolts that opening will get bigger and the squeak should stop. At this point its worth a try .

Let us know how it goes .

Oh, and I have long tubes. They are new ceramic coated Flowtech's.

[Lattimer]

Originally Posted by 4x4toy

Are you running a PCV valve? If so pull it out of valve cover to see if noise goes away. If goes away check for broken or wrong valve. Had engine with faulty valve pull too much vacuum on crankcase and front and rear seals would chirp/squeak.

I'll try that too. PCV is new as well, but certainly could be the issue.

[Lattimer]

I gave up. Took the truck to a local shop to get a new exhaust installed, and have them looking at it to find the noise. First time I have used this place, but they come highly recommended, and they seem to work on a lot of old stuff.

[GASoline71]

Could also be a cracked flexplate or flywheel.

Gary

[Lattimer]

The shop called and said they think its coming from the throwout bearing. Must be the clutch isnt releasing all the way and the bearing is staying in contact all the time.