[MatrixDweller]

They make vibration isolation kits for projectors. i.e: http://www.htmarket.com/vibab.html

I don't have that problem with my projector, but my pot lights flicker when my kids jump on the floor above. The joists in my house are only 2x8's wherein something thicker might be better.

 

[MatrixDweller]

It's probably screwed into the joist though I bet. What you could try is putting a neoprene or soft rubber washer between the ceiling and the mount where the screws go though the ceiling.

If there is still a some movement a home made vibration damper could be made by adding a bracket with neoprene or soft rubber in between the mount and the ceiling. The projector mount screwed into the bracket and then the bracket into the ceiling. That way the screws that secure the mount don't transfer vibrations from the joists/ceiling. With that description you probably get the idea and could come up with a plan of your own.

If there is a lot of vibration then more damping is needed. One thing to consider too is that excess vibration transferred into the projector can also damage the bulb and could make it fail prematurely.