"Strange" noise on 1998 Jimmy

Recently, my wifes '98 GMC Jimmy has started to make a "chattering" noise after putting it in "D" and taking off. It also makes this noise periodically when backing up as well. It almost sounds like a metal-on-metal sound, and doesn't bog or jerk when driving. Also, after driving a bit, the noise seems to subside. But after driving a bit and coming to a stop, like at a light/stop sign, and then taking off again, the noise comes back, particularly while RPM's are up in before shifting (auto trans, 4.7L V-8, 150,000 miles). I checked the drive shaft and it doesn't appear that the U-joints are loose/bad. The drive shaft to the transfer case seems to turn freely when in 2H ; Trans fluid is still red and at proper level. Also, I get the noise whether in 2H or 4H. Lastly, the noise is not there when in "P" with engine running/revving, so I'm assuming it's a drivetrain problem, but not sure where to start looking.

Any help would be greatly appreciated. Don't want to have to go to the dealer if possible. I pray it's not a transmission problem, or if it is, a small one.

Thanks for any replies in advance. Andy

. . Top Post . .

Check your motor mounts and tranny mount first. Engine torque could be causing them to lift up.

A Question for you, Will it make the noise, a noise, or a simplance thereof.....if you hold your foot on the brake while reving the engine up in Drive or Revearse?

(don't overdo this test...it heats the tranny kind of quick like)

MarshM Recently, my wifes '98 GMC Jimmy has started to make a "chattering" noise after putting it in "D" and taking off. It also makes this noise periodically when backing up as well. It almost sounds like a metal-on-metal sound, and doesn't bog or jerk when driving. Also, after driving a bit, the noise seems to subside. But after driving a bit and coming to a stop, like at a light/stop sign, and then taking off again, the noise comes back, particularly while RPM's are up in before shifting (auto trans, 4.7L V-8, 150,000 miles).

I checked the drive shaft and it doesn't appear that the U-joints are loose/bad.

The drive shaft to the transfer case seems to turn freely when in 2H ;

Trans fluid is still red and at proper level.

Also, I get the noise whether in 2H or 4H.

Lastly, the noise is not there when in "P" with engine running/revving, so I'm assuming it's a drivetrain problem, but not sure where to start looking.

Any help would be greatly appreciated. Don't want to have to go to the dealer if possible. I pray it's not a transmission problem, or if it is, a small one.

Thanks for any replies in advance. Andy