RT1000i subwoofer hum

[Boatboy]

Thanks for these great forums - learning lots here.
After some happy years with my RT1000i mains, last night one suddenly started humming loudly (after only two beers... cheap date). I've isolated it to the powered sub. Only unplugging it or turning the Auto/Off switch to Off stops the hum. Swapped channels to be sure, and it's definitely this speakers' sub. Top of the speaker is working fine. When sub is switched on, hum starts out low, but rises in volume as low frequency source sounds increase. Hum is continuous.

Along with this hum, the low frequency info that's supposed to be there is still there, and if a big low passage comes along I also get a sound almost like water gurgling down a drain (have fun with that description!).

I've generally had my receiver volume at 8 to 10 o'clock, rarely at 11:00, and never above. The sub volume controls on the speakers have been at 2 or 3 forever.

Appreciate any help/advice on this.

Thanks, Brad