Hey everyone, I have had a problem from the start with a hum from my center channel on my HK AVR520. I have tried the following: 1. Plug center speaker into different channel (no prob) 2. Plug diff speaker into center channel (lower hum) 3. Unplug all inputs, and turn off TV, DVD, etc. Still a hum. 4. Plug unit into different wall plug. Same hum. I am using Infinity Entra I's as front / surrounds. I have the Entra Center II for the center. How can I determine if it is the unit (requiring service) or an electrical / grounding issue in my house? Has anyone else had this problem? Thanks. Dan G.