I just came home from some time away, and of course the first thing I did was power my system back up.
So tonight I was just sitting quietly going through some mail when I heard a periodic, very low level hum coming from the direction of the P15. Sure enough when I crouched down I heard it coming from the P15. It sounds like transformer hum, but has a sort of periodic oscillating character to it, rising up about every 6-7 seconds.
I ran the Clean function and it seems to have lowered the sense of it, but I don’t recall hearing this when the P15 was first installed.
When I say it’s low level, I was about 8’ away and the sound was just within my range of picking it up, but I did. Incoming THD is 7.7%, outgoing is .7%.