Thanks for all of your suggestions.
I've ordered a 5 meter power cord to check out the amp being connected directly to the wall. All of my wall outlets have 15 AMP PS Audio PowerPort Classic as outlets within them.
The sensitivity of my speakers are 89 DB, so if the problem persists or I suspect driving my speakers is too much for 80 watts per channel, I can get a second one and switch each to mono power amps with 300 watts.
I will hook up the power cord middle of next week and report back.