If you think it's the motor mounts but don't want to spend the money if they're not needed, you could switch the motor mounts from the left to right, and right to left. The mounts get worn down on one side for each of them, so swapping them gives you more life out of them.

Or you could buy a new set of GOOD mounts and if that doesn't fix your problem, keep the old ones as a still-have-life-left-in-them backup pair for when the new ones give out a few years down the road.

They're fairly easy to change out on my car 1991 300d, but ....don't get your fingers stuck in there. Jack it up and be safe.