I just moved my sub from behind the TV to behind the couch for space reasons. I ran wire up one wall, through the attic and down another wall. Now the sub woofer humms when the amp is off. It's a sperately powered sub. It never used to hum when it was behind the TV and it doesn't hum when the amp is on. I'm thinking that my sub speaker wire is laying across a power line in the attic and that's the source. Any other possible causes? Is there a way to sheild a section of the wire if I can't avoid the power lines? The line for the sub went from less than five feet to a 50 foot line. Is this a problem? Thanks.