Bob, some artifacting will be present when using any digital device, DSS, DVD etc... but how much you are seeing I don't know.

The type and amount of signal compression used probably affects how much you will see. DirecTV could probably arrange their broadcasts filling transponders more full which could be degrading picture quality, but signal strength will not affect anything as you will either have the picture or not.

What model TV are you using and are you using the S-Video connection. This won't help artifacting but will improve picture quality on all but the XBR TV's which have a better comb filter.

I think I have heard the noise you are referring to but I can't remember why it happens. It might be a non-stereo source feeding into the pro-logic decoder. Are you using audio patch cables diret to the receiver? You should not have to use the RF connections at all with the exception of the cable signal coming in. You aren't feeding audio from the DSS through the TV are you? The Sony's can be problematic in that area.