This is a good question.
One thing I don't understand is why don't more people have this issue?
One would think if two customers were watching the same channel/show, that they both would notice them/it.
Along this line: During the testing of the HR24 and its DD5.1 dropouts, I've had someone else record the same show at the same time.
I played it back with the internally generated dropouts.
He played it back and heard none.
Had my HR24 replaced and then new one did the same thing, so it didn't look like bad hardware.
The Firmware was found to be the cause of it and has been fixed.
Why could someone else with the same hardware & defective software not hear what I did with every recording with DD5.1?
Maybe some of us simply listen better than others.