Subwoofer Buzz

Hi.

I have a lovely Monitor Audio Silver RSW12 Sub I have had for about 10 years or so. It's been pretty much flawless since I got it.

Recently it's started making a noise I can't seem to get to stop. I don't believe anything has changed in my set up.

I've attached the recording. Disconnecting the Subwoofer cable from the amp doesn't make any difference. I haven't touched any of the other switches on the back, but I have attached a photo of the settings on the back in case a kid has knocked it or something accidentally. I also changed the power cable and power source. Turned on, with no cable for the amp plugged in, it makes the noise. Once it made this noise for like 6-8 seconds and then stopped, but when I turned it off (which makes a very loud thumping noise) and back on again a minute later, it made that noise and didn't stop.

https://soundcloud.com/networkn/subwoofer

I am assuming it may be faulty. I called the distributor today, they made mention of a board that might have failed, and that for $1000 they can replace that board with the latest version, from the current Silver Sub, and it will get "upgraded". I am not sure what difference that would make, but considering replacing this like for like would cost $2500, $1000 seems "cheap". I am hoping someone has fiddled and I won't need to spend anything.

Any assistance would be gratefully appreciated.

I have also read online this could be because of a ground loop, but I am unsure how this could now be an issue when it wasn't previously.