Loud buzz and hum in my REL subwoofer

Call Sumiko. I had the same issue and the lady at Sumiko that specializes in REL products (don't recall her name) knew exactly what to do.

I had a similar issue with my Strata III some time ago; turned out to be a bad connection in the neutrik connector. I would definitely try a different cable before moving on.

Best of luck.

Randu

Classic case of ground loop hum. Removing the second ground from the sub power cord will solve it.

I Would try a different cable first.Also if you have some other preamp,or receiver(any thing with a variable output) ,try that too.When the receiver is turned off,most subs power
down.If the interconnect wire broke loose inside from moving things do to cleaning etc.,the sub woofer could recognize stray AC,or RF signals causing the hum and keeping it powered up.

Your amp is probably going out unfortunately... I had a Storm do the same thing then driver went out and the cone assembly had to be replaced so I returned it to the dealer. They are not built very tough like JL Audio Fathoms are for example. Or you might just have a new ground loop issue. Try a a cheater plug or move the Rel to another outlet or move some lights that are plugged into near outlets for example to isolate it.