P20 slight hum

I was close to my P20 unit today and noticed a faint hum noise coming from it. It doesn’t present in any of the other equipment. I unplugged all other equipment and restarted. It is still there, and I can hear from about 1m away when there is no other noise. If I power the unit off, then turn the physical switch on the rear of the p20 on, it momentarily makes a louder hum, then fades to a slight hum.

Does anyone have any advice? I’ve had it for about 4 years since new.

Thanks in advance,

Andrew

I have a clear hum from my P15 also.