Rattling noise from engine but only in gear

[94silver280]

Hey everyone I have a 94 c280 and it has a noise coming from the engine. I've done some research and figure it might be a tensioner, but it only makes the noise in gear. It sounds like marbles. Anyway If I shift to neutral or park the noise goes away which leads me to believe it may be coming from the transmission. I have 140k on the car and no problems at all. It drives and shifts fine. I'm not sure of the service history, and this is my first mercedes. I haven't gotten a stethoscope to check exact location of the noise yet. Figured I'd ask around first. Any input would be greatly appreciated! Thanks

[W202FTW]

Hey everyone I have a 94 c280 and it has a noise coming from the engine. I've done some research and figure it might be a tensioner, but it only makes the noise in gear. It sounds like marbles. Anyway If I shift to neutral or park the noise goes away which leads me to believe it may be coming from the transmission. I have 140k on the car and no problems at all. It drives and shifts fine. I'm not sure of the service history, and this is my first mercedes. I haven't gotten a stethoscope to check exact location of the noise yet. Figured I'd ask around first. Any input would be greatly appreciated! Thanks

Get under the car with a small rubber mallet and start tapping away, could be a transmission mount or even a heat shield rotting away. If you think it's from the engine pull the belt off (you'll need a fan clutch tool to do this) and start spinning away the pullies and listen for anything that sounds rough.