While tweaking this afternoon, I heard an odd sound in the 612M. As the signal from the axe-fx/guitar decays, a strange frequency sweep appears on top of the guitar tone. I'm not sure how to describe it. It sounds kind of like the filter sweep you get when tuning an am radio. It starts high and then sweeps lower as the signal continues to decay. You can't hear it at all at normal volumes - only at minimal vibrations, like when you're rubbing a string on a fret with vibrato at the very end of a note trailing to silence. It sounds kind of like "heeeeuuuuuu". I only have one of the 612's hooked up right now as I wanted to wait to open the other until I was sure I was going to keep them. I may open the other later, but may opt to just take them both back and have the dealer assess it. It occurs on all patches but only through the 612. I hooked up to an Event PS8 and heard no trace of the sound whatsoever.
It occurred to me that this might be an effect of digital class D amplifiers. Has anyone heard this kind of thing before? It's very faint, but definitely a deal killer for me if it's normal behavior. There are times when I play very dynamically, using the sound of the string(s) on the frets to get a certain effect. The sound is audible when at that dynamic level. Of course, there's also the principle of the thing. If this is normal, then the unit is poorly designed.
BTW, I was very relieved to confirm that it was not the Axe-Fx.