Truck make a noise I dont like -HELP-

[PHOENIX]

My truck has been making this noise lately.
A few weeks now. Doesnt seem to be getting worse.
It only does it when accelerating.
Not very noticeable from a stop, but when you go to second gear it can be heard.
I have a manual transmission.
I do not really hear it from second gear to third.
When a vehicles timing is off and you turn it off you get that brrrrrr sound.
It kind of sound like that brrrrr, but not as loud.
I notice the sound most when I am turning a corner and do not down shift into first.
If I keep it in second and start to hit the gas it makes the brrrr sound the loudest.
My truck has had an oil leak for awhile and it did get below the add line once recently.
But it was making the sound awhile before that and doesn’t seem to have gotten worse.
I do not know what this is, is this a valve sound?
I am going to check my timing and a few other things later today hopefully.
Could a sloppy transmission cause this sound? My trans is rather old and has been through a lot.
It is a little sloppy and sometimes clunks when I put it in gear.
The sound seems like it comes from the engine bay, but its hard to tell.
It only makes the sound when driving (under load).
Truck seems to run fine and strong (well as strong as a stock 350 could run).

What do you guys think this is?
What should I check to help figure this out?
Thanks

[Slonaker]

I used to have a 305 that would make a rattling sound under a partial load. It sounded a lot like a knock. It turned out to be the heat riser, or whatever the little vaccum operated thing is on the passenger side exhaust. It would rapidly open and close under partial accelleration. I never figured out why, but it went away when I pulled the vaccum line off of it.

Slonaker

[PHOENIX]

I check that out. I have had the vacuum line off forever. I wonder if the valve inside is still moving around. On my lunch break I was driving home and playing around with it. I got it to do it a little worse and it kind of sound like exhaust. I am going to check the EFE when I get home.

Any other ideas?

[85Silverado]

no...with the vacuum line off it stays open. It's spring operated and the vacuum is what pulls it closed...so with the vacuum off it should be open unless it was ceased shut or partially closed.

[Bowed]

I agree you should check the timing .

[Bowed]

I'll add one more thing . I'm really begining to suspect the quality of the gas we are getting here in Pheonix .

[PHOENIX]

Well I hooked up the vacuum gauge and tach/timing light last night. The vacuum seemed ok, once the truck was warmed up, it was at 20 with a slight flicker back and forth (19-21 or so). The timing however was way off. I had my timing set at 10, it was a whole timing marker off (something like 24 or so). I didnt use the feature on my timing light to figure exactly how far it was off becuase I just started trying to get it right. I got the timing back down to 10 and it would slightly move down towards 8 when I reved it. So I tightened the dist. hold down bolt and tried it again. I reved it up and the timing would stay high, like 16 or so, then slowly drop back down to 12 or so. But wouldnt return to 10 as I set it. So I tried it a few more times and got it to stay around 8. So I took it for a drive. Truck ran much smoother (I guess I didnt realize it was running a little rough) and had a little more power. NO NOISE AT ALL. It was great and late, so I couldnt drive around to long. There was no traffic so I was flyin. Drove to work this morning and everythimg seems great. I need to check my timing again to see where its at now. I am going to start a new thread about timing changing.

Thanks for all your help.

Ohh yeah I checked the EFE and it was locked in the open position and the spring is tough. It took a good turn on the lever to get the valve to close. Also I hear a slight exhuast leak over on the passenger side. Sound likes its around the manifold, cant tell where for sure.

[swervin ervin]

Pull the cap and check the advance springs and weights. Sounds like you have a problem inside the distributor somewhere. For sure doesn't sound right to me. As I'm sure you know, anytime you move the distributor to change the timing, it should jump to the mark instantly. Might be a bad vacuum advance canister or something. Strange indeed.

[flip66]

you might want to check the EGR it works off vaccuem to close it but it has a spring that holds it down when there is no vaccuem it might be worn out. I have seen it cause really strang things to happen. Even if its not hooked it could leak and cause problems.