Accepted Answer

Hi, I will try to assist you with this.
First thing that comes to mind is broken engine mounts. The rubber separates and allows the engine to move all over the place, and could tweak up and hit the hood under load. The mounts ae cheap about $40 for the set, and a couple hours labor.
Easiest way to check is with a prybar lifting up on a solid point between the engine and subframe. If it moves alot, the mounts are bad.

Also it could also be a broken fan blade, or off balance fan that could cause a vibration. Inspect the fan, and make sure all the blades are there, and that it spins freely.

If it seems like the problem is the engine itself, it could be misfiring alot. This could be caused by spark plugs being worn out, old plug wires, old distributor cap and rotor.

Also poor valve adjustment can cause weird things too.

Expert:	bimmaster
Pos. Feedback:	100.0 %
Accepts:
Answered:	10/22/2009

BMW Technician

3 years dealer experience, master bmw tech