My car has not been lowered at all. I did consider that the fan might be striking something in the car, and thought that maybe it might be the shocks, but that would not explain the sound. My car is in the shop right now for a fairly major repair (wiring harness, throttle valve actuator). I'll have him look at the engine mounts to see if they are worn out. At this point, I told him to simply keep the car as long as it takes to get everything right. They gave me a 300E as a loaner, so I don't really care how long it takes.
Thanks for the suggestions. If anyone comes up with something else, I'll be happy to pass them along to my mechanic.