Hum from 6250 Receiver

Slight hum from my receiver. It happens in all modes and does not increase with the
volume control. I'm new to this receiver as I got it off of Ebay about three
weeks ago and never noticed the hum before yesterday. Any Help?

It would be a good idea to check the grounding of all your equipment, and it's proximity to other elctrical sources ie: Televisions. Also make sure your power chord does not cross over or intertwine with your speaker wires at any point...These are basic tips I picked up along the years, hope they help