Hope nobody minds but I'd like to keep this thread alive. My 990 did this distortion thing almost out of the box. And this week it's happened at least 3 times. A power cycle or two has thus far always cured it. My advice is don't anyone panic and just live with it. It's a minor inconvenience for something that to me, really delivers the goods.
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Living Room: Outlaw 990-7125. 3 Outlaw LCR's (FL-C-FR). 2 Outlaw Surrounds. 2 Outlaw BLS in the rear. Outlaw LFM-1 Plus Subwoofer. TCL 65 inch Roku TV. OPPO BDP-83.

Bedroom: Marantz Cinema 70S. Aperion's all the way around. Apple TV. HTPC built from scratch.