So I saw this on another forum: As for the MT15 amp I joined a FB group for it after hearing that some of them have had issues with a crazy hum. I did notice some hum when I did my recording but I was direct recording with a load box + IRs and headphones so i'm use to hearing crap you normally don't hear when playing. Anyway, someone in the group talked to the guy who designed the amp at PRS and said they are aware of it and are working on a fix. Apparently when you cram 5 preamp tubes and 2 6L6s in a tiny box it can happen. I was told to try this to see if you have one affected by the hum: Unplug your guitar +fx loop from the amp and just leave the cab plugged in, power up the amp, switch to the clean channel and take it off standby. If you get a hum with nothing plugged in on the clean channel then its bad. So I did the test and there is a slight hum. Nothing that I think would be heard when playing or with the volume up even a little, but it is there. The odd thing I discovered was when trying to run stereo or with a slave amp. So first I tried to run stereo with a 60 watt tube power amp. Send of the MT15 into a stereo delay pedal. One out of the pedal back to the return of the MT15 and the other out of the pedal into the power amp. Weird thing is I get no signal going to the power amp. So next I try running a cable from the Send of the MT15 straight into the power amp. Problem is with a cable connected to only the send and nothing connected to the Return there is a very loud noise very similar to unplugging the cable to your guitar and touching the tip. I have run several amps this way or to go from the Send straight into my interface. Can any other owners try this?