My Ashdown Labs MK500 hums a lot more than it should. I played at a bar with questionable power the other day and the hum was disastrous. I had to play most of the night with my high end rolled way down. For background, the amp has got no ground lift switch, and I use a Furman PL-50 to no improvement. I'm not looking to re-create all the threads on this board about how to address ground hums - I've read those and there is good information there. I'm really just wondering if anyone else has had a hum issue with this particular head, and if so what you did about it. Thanks.