After some futzing around with the settings, I figured out why I was losing the signal on the HDMI connection from DTV HD-> Samsung HT AVR-> LN46A550...
As I suspected, the DTV HD receiver was cycling through the different resolutions every time I changed the channel (Native Resolution)...it went from 480i, 480p, 720p, 1080i... in that order. Whenever the DTV would switch to 480i, I lost the signal, but if I change the resolution to 480p, 720p, 1080i, I got the video back. I assume the HT AVR cannot process the 480i...easy fix, set the DTV to NOT feed 480i over the HDMI.
As far as the Audio crackling, I tried changing the HDMI cables to higher grade (1.3 compliant) cables, downloaded and updated the firmware, but no luck! I seems to occur when turning on my AV receiver and there is no feed from the DTV or when switching the input source on the AV receiver. At one point, I decided to bypass the AV receiver and plugged in the DTV directly to the TV...and noticed that while the DTV was downloading a software update, the crackling returned...once the programing started, the crackling stopped. It appears as if the TV is picking up some type of signal or static while the source input is off.
From what I've read on this and several other forums, I'm not the only one with this problem and it speaks poorly of Samsung as to why they haven't resolved these issues.
After all, HDTV as been touted as the holy grail of televisions and it's very disapointing to know that I get better sound out of my 36" analog TV than I do out of my $1500 46" digital TV!
I forsee a return trip to best buy and swapping this TV out for a SONY instead!