Last week my truck (04 GMC HD 3/4 ton duramax) started making a vibration/noise. It happens when under acceleration and around 2500 RPM. It is really noticeable on the highway at 75 to 85 MPH. It eases up immediately though not completely when I let off the accelerator. Below 70 it is not to noticeable. It will do it at slower speeds as it shifts through the gears, always around 2500 RPM, it has the Allison auto transmission. There is no noise when turning and I don't feel it in the steering wheel. Thank for any suggestion you might have. Jay

so did you rule a wheel bearing out? Just a shot in the dark here, but my brothers truck also a vibration. When we tore the truck apart to do his injectors we were tracking down a coolant leak and noticed his harmonic balancer had a nice size chip in it. Like I said....prolly a long shot.

My guess could be u joint starting to go bad

i agree. u joint, wheel bearing, or carrier bearing

If it happens at the same engine speed in multiple gears, I'd guess your problem is not downstream of the tranny. Might be damaged engine mounts or a problem w/ crank balance (including damper, crank, rods, flywheel, torque converter). Might also be one cylinder that's a bit weaker or stronger than the others.

I should note that I have zero experience w/ any of this - just thinking things through.

U joint, wheel bearing, or carrier/support bearing (if you have a two-piece driveshaft).

Moved to Drivetrain

Mount getting soft and letting the exhaust touch somewhere possibly, if not that then like the others said check driveshaft u-joints and bearings. I would also check wheel bearings just because you should check them frequently. Good luck.

Most driveshaft vibration issues fall in the 35-45mph range.....So, I'm thinking tire balance. Troublesome wheel balance issues can best be sorted out with a Roadforce balance.

The front hub bearings can be checked for wornout by jacking thhe truck and rocking each front tire assy at 12 and 6 O'clock. There shouldd be zero movement when rock at 12 and 6. Rocking by grabbing at 3 and 9 O'clock will reveal if there is any steering linkage looseness.

Thanks for the idea's. Yesterday, when I pulled away from my office, next to a wall, I notice a sound like a popping or (rock in a can sound). I was able to repeat this multiple times. I looked under the front and the passenger side CV boots had grease all around the shaft and the outboard boot. I hope this is the problem. A good friend has a tire and alignment shop so I dropped it off with him this AM. I am replacing the CV's and wheel bearing on both sides while I am at it. I just had the heads replace by the Chevy dealer 4000 miles ago. I hope it is not a problem with the motor. I did seem like it was dropping a cylinder at first, kind of still does!! May have more that one problem going on. Man I can't catch a break. I will post an update later today. Thanks for everyone's help. Jay

Ok, just got a call and the rear U-joint was going out and the CV-joint on the passenger side was bad also. He said it needed upper ball joints, tie rod ends, and a couple of other things as well. Yea!! I can't complain to much, it has 140 K miles on it. Thanks again for the help. Jay

did you get vibration fixed?