adk, sorry if I missed it, but the buzzing happens always, with music being fed, in stereo, in mch, in mch matrixed, etc?
Just curious because I think I may have buzzing only in the rears (not sides) when feeding stereo? Something like that, and it almost never comes up since I never use stereo w/o matrix in the HT (have a dedicated stereo system). Soon as I matrix, buzz absolutely gone. I know, weird.
Of course in your shoes, since it's brand new, I'd exchange/return.