I got my brand new Marantz PM-7200 about 2 months ago. It sounds great, but recently I noticed what sounds like transformer hum. I put my ear up to all my other amps/receivers and they all hum, but the 7200 is audible from across the room when nothing is playing. I disconnected everything from it, and the hum is still audible. My dealer said they would swap it out, but what if the new one is exactly the same? Should it be quiet or is this normal?