highway noise

[halfadeuce]

So last Sunday I was driving back from the Pomona swapmeet and I noticed a type of groan noise from my suburban at highway speed. It's not a clunk or grinding noise. It sound familiar to tire noise but it goes away if I let off the throttle or if I'm above or below about 1800 rpm. I can't tell exactly where it's coming from. I was thinking either water pump or power steering but I'm not sure. Anybody know what it can be? Also I noticed that the hose from the pcv to the bottom of the carb was collapsing when I give it throttle. I replaced the pcv but am not sure if that can be related in any way.

[magicoolbus]

I would say if it is the PS pump, during turns, the pump would groan and make the noise you are hearing but in a louder fashion. Do you have a fan clutch between pump and fan? After the engine is at temp and engine is turned off, grab fan and see if there is any resistance to turning it.

[halfadeuce]

I can describe the sound as similar to a heavy fan with the clutch but I'm running electric fans.

[Alex V.]

Exhaust leak in just the right spot or bad u-joint?

[AzDon]

I experienced something similar a couple of weeks ago..... at about 70 it was as if I was driving on a rumble strip and would stop if I backed it down..... When I put my burb together, I had converted to a one-piece driveshaft and had not checked the u-joint angles..... Proper angles should be less than 3 degrees on each u-joint and the 2 u-joints should have the same # of degrees.... I addition, the trans tail shaft and pinion shaft should be on parallel planes.....It turned out that all I had to do to achieve these specs was put a 5/8 inch spacer under the trans mount and OH WHAT A DIFFERENCE!.....
To fully grasp the concept, do a google search... lots of diagrams and such!

[61superman]

agree, mine was pinion angle only at high speeds corrected and no problems since

[halfadeuce]

Update. I ended up servicing the rear end a couple weeks ago. It was very very low on gear oil. There were 4 small pieces of the clutch at the bottom of the dif. The gears looked fine and after topping it off it still made the slight scraping sound. I have had it parked since then and noticed a leak coming from the front of the rear end where the driveshaft yolk attaches. Could the seal be what's making the noise? Possibly scraping on the rotating yolk? Also will I be able to continue driving it if I take care of the leak or is it gonna blow up on me due to the little pieces of clutch I found.

[halfadeuce]

I replaced the rear pinion seal and no more leak. I drove to work today and I still hear the sound. But it sounds more like a whistle coming from the drivers side engine by the brake booster. It's really hard to tell because I only hear it while driving. It won't do it in park. It comes in right around 1500 rpm and goes away by 2000rpm. Any ideas?