Barely audible hum from P15

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%.

Mine makes a very slight hum, too.

Fan on?

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.

Fortunately, P15 does not have a fan :pray:t2:

Definitely try what Serhan mentioned. I’d also be curious if you still hear it with nothing plugged in the back except its own power cable.

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.