Been having problems with one (of two) HR21-700s. Very slow response to remote commands. Very slow to do anything. Lately while playing recorded programs the playback has frozen for 15-20 seconds, then continued. This is happening more and more frequently. I've reset the DVR (RBR) and it has not helped. Overnight I unplugged it, and when I plugged it in the morning it got stuck on "Checking Satellite Signals". Other two DVRs (HR21-700 and HR20-700) are fine. Any suggestions before I call DirecTV and ask for a replacement? Thanks!