Might sound stupid, but make sure nothing is getting in the way of the pulleys and check your motor mounts too? Unless you're like 100% sure it's coming from the internal aspect of the motor.
Got any check engine lights on? Also, make sure none of your wires are touching the manifolds or anything like that. Timing could also possibly be off.
Err.. if none of that works.. drain the oil out, refill it with gear oil and slap a for sale sign on the windshield.
