Speaker hiss that increases as volume increases.

I have a Sony STR DG 2100, Kef 2005.2 speakers, PS3, APC C5 power filter all connected together via generic hdmi to a Samsung LN46A650 and with quality monster speaker wires. I watch Blu ray movies all the time and there is one thing that keeps it from (relative) perfection: When I increase the volume beyond -15 or so I hear a significant hiss that fades in and increases progressively with the volume. I added a power filter and although it had some good effects it didn't do anything to the hiss. Next I cranked up the volume to where I could clearly hear the hiss and and individually disconnected and unplugged each component and speaker from the system to see if I could isolate it, but found nothing. Next I rechecked the electrical to make sure the sockets are grounded properly and they were. I next plan to run a cable from the grounding rod buried outside my HT room to the receiver. Any ideas on what could be causing this? I hate watching movies quieter than I would like to just to avoid a hiss, especially with those TrueHD movies recorded quietly.

I adjusted the equalization and that helped quite a bit but it also lowered the overall volume and I think effected the sound. It's better than the hiss but it seems like should be able to have the equalizer above flat and remove the hiss, it's so annoying in I Am Legend in the quiet scenes and then it gets loud and it's not loud enough. Any other ideas? I'm hoping MichaelJHuman isn't right because that means a new receiver and I'm not looking for that yet although those new Denons sound so nice.....