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%.
Try to switch it to Sine instead of Multi, then restart and watch THD out and listen for hum. You can go back to Multi after restart. If I switch on with Multi, THD out reaches 1.2%. With Sine it reaches 1% only.
I think I found the cause. It only seems to happen when my plasma TV and set top box are powered up. They are also being fed by the P15. If I turn them off the cyclic humming is no longer heard.
