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Can of Marbles - only while in gear

Hello all you wise auto people…

My 1999 Chevy Suburban K1500 4WD has recently developed a noise that sounds like a can full of marbles being shaken.

I have read many posts both here and else where (sorry Tom and Ray) and most surmise that;

- Catalytic converter may be bad

- Timing issue

- Low octane ping

- Loose Heat shield

The fly in the ointment is that this sound only happens when I am accelerating in gear. It mostly stops when I coast. The sound stops if I shift into neutral, even if I give it gas. So I am assuming that it shouldn?t be any of the above.

The sound is coming from under the car and since it only happens while driving I can’t be more accurate.

No work has been done recently and the only observation is that I noticed a few drops of fluid on the driveway under the rear differential.

Any help you all might have would be greatly appreciated!

My vote is for low octane ping . . . check the ignition timing also. The CAT going bad in a '99 is unlikely, but possible. A loose heat shield is easy enough to check, get on your back and shimmy under this truck . . . you won’t even need to jack it up. Good luck! Rocketman

Check your fluid levels in the transmission (if this is a manual), the transfer case, and the rear and front differentials. It sounds like you might be losing a bearing in one of these units. It has to be a bearing that loads under engine torque.

Hope that steers you right.

My vote is for spark knock (octane ping).