I own an ASR 10 rack sampler. Every now and then I get a buzzing sound from the unit even with the power off. But the main switch is still on. The buzzing goes off when I switch the main switch off. Anyone encounter this with their ASR before. Any help will be great. Thanks.

Do you have a proper ground? I had an EPS 16+ ru that buzzed and shocked me when it wasn't gounded. So did my ASR-10 board. Put the underside of your arm on the metal casing where a screw is. If you feel a very slight tingle you need to ground it. You could also get a ground tester for your wall outlet.

Ground it!