Remote trouble on hddvr

I have an HR21-700 and lately I have been having trouble with the remote not responding. I thought it was just the remote, so I got the spare remote and tried that one, it works, but only sporadically. I reset the first remote (an RC-65R) and it works for a couple hours, then stops working again. So after trying to reprogram it a few times and having it stop working again, we just bang it on the edge of the couch, and it works again for a little while. I've tried rf remote and it actually seemed worse. Is it just the remote, or could it be the receiver?