If Im just cruising at around 60 in 6th gear and I have the pedal pushed in 1/2 an inch or an inch to maintain speed. I get this whine noise from the back, and if I modulate the throttle the sound will follow. However if I push the pedal in further to the point where the engine is underload now it will go away. I dont hear it during city driving, likely because the pedal is pushed in more.

 

You sure it isn't the differential/gears?

 

I'm with injuneer on this one. When was the last time you changed your rear diff fluid? How many miles on the car?

 

Definitely differential/gears - no question.

 

Im pretty sure its not the rear differential/gears, because if I just move the gas peddle a 1/4 inch I can change the whine noise pitch, and if I push the pedal in an inch it won't make any noise. It's only when im cruising at a constant speed and the pedal is barely being pushed down (just enough to maintan 65 in 6th gear), if I take my foot completely off the pedal the noise will stop instantly, and if I just push the pedal in a tiny bit it will come back, untill I push it in maybe an inch and the engine comes under load again then it will dissapear.

I changed my rear diff fluid about 25k ago, the tailhousing does seap (like all fbodys) and I just recently pulled the filler plug to check the level and oil still came out, but I still squirted some fresh stuff in and closed her up.

 

Still sounds drivetrain-related to me. The pump runs at constant voltage/pressure. It won't change with throttle position. Had the same thing happen to me.

GEARS/DIFFERENTIAL!

 

hmm yeah that does make sense, for some reason I thought that fuel pressure/pump pressure changed at throttle position. Is gear whine like that a good sign that my rear is about to take a crap? Or do you think an oil change + the GM additive will fix it? The last time I did the rear oil I put the additive in.

 

The gear whine is not a good thing. Your first thing to do is to change the fluid and put some gm limited slip additive in. Do NOT use any other brand than the GM stuff. You may also want to consider using synthetic gear lube. Double the price but it the whine is bearing related, could make a difference.

HTH


Andy Schuck