Okay, so a few months back I bought a 6505+ head and paired it up with a Marshall 1936 2x12. Works great, sounds great. I think I've finally achieved the tone I'm looking for. Recently though, I've been getting some weird kind of feedback or something while I play. It's kind of hard to describe what it sounds like, but the closest thing I can compare it to is a bomb dropping. It starts off like a high pitched whistling and gradually goes to a lower pitch until it dies out. It's really annoying because I can hear it right through my playing. I have no idea what it is. It happens at random times, every minute or so. It's weird because it never happened until just the other day. I thought maybe it had something to do with my Boss GE-7 that I just bought last week, but it doesn't matter whether the pedal's on or not. It still happens. The only other thing that has changed in my setup is that I bought a Boss power adapter and some Ibanez 5 way cable so I could power all my pedals with one adapter.

I guess basically I'm just asking if anyone knows what it is/has experienced this before/knows how to fix it. Thanks in advance.
Have you checked if it does it when the pedal's not in the signal chain at all? It's probably not true bypass, I'm not sure if any Boss pedals are, so if it's something weird from your power supply then it could be coming through when the pedal's plugged in but off.
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I tried taking both Boss pedals (DD3 and GE7) out of the chain and the same thing still happened, although less frequently it seems. The other pedals I have running are a Decimator and an Ibanez TS9. I've been playing for a few minutes without the power adapter plugged in though (as in the pedals are just running on batteries) and so far, haven't heard it yet. I think that might be the problem. Not sure if it will make a difference, but I'll try plugging into a different outlet. I was using my computer's powerbar before, if that would have anything to do with it.
move the ground rocker switch in the + or the - position thats what the manual says to do if you experiance any humming