My 600 did that as well, and I removed the gound screw on the back, which was an option back in the V2 series, not sure the 500 has that on that back, hmmm. If you unhook other equipment from receiver, and add them back one by one, I wonder if one of those items is causing the issue. Possibly the HDMI on the Ps3. Ground Hums suck.

M80s VP180 4xM22ow 4xM3ic EP600 2xEP350
AnthemAVM60 Outlaw7700 EmoA500 Epson5040UB FluanceRT85