Reception jumps up and down every 5-10 seconds...phone now almost unuseable!

Hey guys...I've looked all around the internet to see if anyone else has had this problem with their HTC, but no luck!! 

What's happening, is that when I look at the signal bars on my phone, they will drop down to nothing for 5-10 seconds, then spike back up to normal for a few seconds, then back down to nothing for 5-10, etc. 

It seems that I can still make outgoing calls with the phone...but I don't receive a good percentage of the incoming calls or incoming text messages.  This has resulted in having to go back to my Razr for the past couple months!!  NOT GOOD!

Any ideas on what may be causing this??    

This didn't fix it.  I've changed PRL's several times.  It seems to be a mechanical issue as I've even updated ROM's.  It may have been the result of dropping it...but why would that cause the antenna to go haywire??  Any ideas of a fix?  Has anyone ever opened one up and tinkered?