I've had my DT50 212 for about 6 weeks now, and it's been great up to this point. For at least the last week it been sounding...not right. The sound quality has become poor, almost muddy or not very well defined. It's especially noticeable on the high gain topologies. Also, in full volume mode I usually have the main volume knob at 2 o'clock. When I turn the channel volume to 12 o'clock or higher I get a horrible squeal or feedback type sound of some sort. Does it even when I have the strings completely immobilized by my hands, in both channels and most topologies. I have very limited experience with tube amps before this one, so I'm not sure what it could be. I've tried a couple of guitars with this, my Ibanez S570, and my JTV 89 and it's the same for both. I do also have the latest firmware installed. I would record a sound clip, but I doubt my cell phone would do it justice. Thanks in advance for any help I get!