Thumping sound coming from the dashboard area...
 

This started a couple of weeks ago and has gotten progressively worse. It appears to be coming from behind passenger side airbag. It starts like a thump... thump.... thump then speeds up to a quicker thump, thump, thump until it stops. I can't figure any rhyme or reason to when it does it, but as of now it happens once every 7-10 minutes.

Any ideas?