I have a Sony STR DB930 A/V Receiver with brand new Polk tower speakers, and a polk center speaker. I notice a bit of static coming from all speakers at low levels (I believe it is always there, just more noticable at low levels)from any/all sources. I replaced my Boston Acoustic's as I believed it was a speaker problem which it is obviously not. I am thinking it must be the receiver but hate to buy a new one. Any advice?