Pulling my hair out with eratic grinding noise

[Misael]

I just got my truck a few weeks ago, on the 1 hour drive home it started doing a grinding noise ONLY under throttle. I then changed out all four rotors and pads, rear differential fluid(had only a quart in it from leaky rtv diy gasket) and still nothing. The front differential oil looks really clean so i didn't bother changing it.

Just got a CTS the other day and i did a highway cruise to check delta and i confirmed it was only in gear and under throttle that the noise would appear. I put it in neutral at about 70 and couldn't hear a blip while giving helds revs at different rpms then I put it in drive and as soon as i start giving it throttle the noise appears

Also, the noise is always apparent at high speeds BUT at slow speeds it's on and off as in i could go through a few street blocks and it wont do it all the time Any ideas?

[Misael]

Going to drain the transfer case this weekend and put some new fluid in it. Checked the driveshaft and everything looked fine, the carrier bearing had some play in it and could see the rubber cracked but I don't get any "thuds" or clunks

[greasyF250]

U joints or possibly a rear axle bearing on its way out

[Misael]

Wouldn't it make the noise under at all times when in drive?

[greasyF250]

usually only on acceleration

[Lumberg]

I experienced a similar situation you describe. My trouble was that my ‘new’ 4-inch exhaust pipe was hitting the chassis. After a little time, the bend over the axle had moved just enough to vibrate against the sway bar. I also noticed the rear hangar was bumping the fuel tank shield. Just a little tweaking of my clamps and that solved my problem. There were some rub marks I found sliding around under there with a flashlight that gave it away. Since I couldn’t pinpoint the source of the sound that seemed to come from the firewall/tranny area, I started checking EVERYTHING. I was very relieved to find this and not an expensive problem. I sure hope yours is not related to something serious.