Hey everyone. I've been searching for answers all over. Nothing that I can find has really matched my issue. I have a GK 700RB head and a 410rbh cab. I've had it for a few years, it hasn't been played much other than a few shows and practice at home. I've been playing it a lot in the past couple weeks without issue. But yesterday a mysterious buzz showed up when I turned it on. The buzz is very loud and you can hear it over playing. troubleshooting I've done: 1. Still does it without a bass or cable plugged in. 2. Volume does nothing to it, and neither does mute. 3. The only knobs that lower the volume of the buzz is the Woofer knob (the boost knob lowers the strength of the buzz, but never gets rid of it completely.) 4. if I press the "woofer hi cut" button in, it creates an extremely loud squeal. Ear piercing. 5. there is also a much higher pitch buzz that is not nearly as noticeable until Woofer is turned all the way down (thus removing the low buzz) This higher pitch buzz is affected by the tweeter knob. 6. Tweeter High cut button doesn't seem to change much with the high pitch buzz. Again, I haven't been playing it hard or anything. it stays in the same spot, no travel. The only thing I can think of that happened before that buzz showed up was a small power flicker. earlier that day. and I leave it plugged in 24/7 (always turned off though.) Any ideas what this could be? cost to fix? Any DIY remedies? Issue with head or cab? Thanks for all the information to come!