Bgoeller, note the most recent post above by Jea48. I agree with him that the findings stated so far are not consistent with the problem being caused by a ground loop.
Good suggestion by Imhififan to see if the 8801 produces a hum when connected to the sub.
One note about muting. When I do use mute there is a "pop" whenever I mute or un-mute the system. Is something I should be concerned about?
Not sure that any of us can answer that, and of course it would depend on how severe it is. I wouldn’t be totally surprised, though, if the underlying cause turns out to be the same as whatever is causing the hum problem.
But on the other hand take a look at
this thread, starting with post no. 245. That poster also had a popping problem with an 8801, which occurred at power on/off, mute on/off, and Audyssey on/off. Some posts later he incorrectly concluded that it was due to an interchange in the 8801’s design of the signals on XLR pins 2 and 3 relative to the USA convention of pin 2 hot and pin 3 cold, which of course would not be responsible for that kind of problem. (At most it would result in a polarity inversion, which on most recordings would be audibly insignificant, and which in any event can be compensated for by interchanging + and - at the speakers or the amp outputs. And if an XLR input and an XLR output are being used it wouldn’t result in a polarity inversion at all, since the two inversions would cancel out). Later in the thread, though, it appears that the popping problem remained, and no resolution was indicated.
Finally, FWIW, in post no. 245 that poster linked to a post by someone else who had a popping problem with an 8801 at power on/off and mute on/off, which arose only after a firmware update had been incorporated in the unit. Apparently no resolution was indicated there either. But that would seem to suggest that if perchance any firmware updates were released subsequent to whatever version is in your unit, updating to the latest firmware MIGHT cure the popping.
Regards,
-- Al
