onkyo tx-nr609 subwoofer buzz/interference query

[Wattogwan]

Hi all,
I have had an onkyo tx-nr609 for a few months but recently the subwoofer has started buzzing (low frequency noise) after about 30 seconds (never happens right away).
I thought it was the subwoofer at fault, as it was 10 years old so I borrowed one from a friend - still happens, so I changed the lead for a new one - still happens!
I have also checked to make sure no other wires are touching so I am now left thinking the amp may be buggered - or have I missed something?

Please help!

 

[dante01]

Try using a multi gang plugged into a single mains outlet rather than plugging the amp and sub into different wall sockets. It could be due to poor mains earthing or a ground loop.

 

[Wattogwan]

Thanks for that- did a few tests and it looks like it is the plug socket that is the problem.

Cheers