Vibration in engine
 

Hello everyone,
Im having a weird problem with my 2000 c280. For a few weeks now i have been getting a vibration in the engine area when the car is idling. If I switch gears it changes, reverse is the worse sounding. When i accelerate there no problem. Im thinking a motor mount is bad but I havent had it checked yet, though I would run it by you guys first. Only other thing that happened was 4 days ago my belt tension pulley collapsed (cut the bearings in half..lol) and snapped the belt. I replaced it but still getting a vibration. Let me know what you think.
Thanks in advance.
Richard