I am hearing the same popping noise. It just started doing it. Mine is in the right front speaker. It is very distracting. It occurs when changing modes or several seconds after the stopping the source (ie dvd, cd, computer etc.)It does with both coaxial and optical connections. I have changed the wires with no change in the problem. This seems to be the preamp as the source of this problem. There is no popping/thumping noise during playback however only when stopping a source or change modes.