After reading the great reviews and receiving advice on this forum, I just purchased a demo 4B cubed to replace my Sunfire amp. It has paperwork showing that it was returned because of a noise in one of the channels. With the preamp off I could hear a slight buzz in the left speaker when I got close to it and a much fainter hum in the right speaker. Both are much quieter than the hum the Sunfire has been emitting. My question is: since I got a very good deal on it being a demo, should I return it to the seller or send it to Bryston for service? Or should I not bother with either because it isn't audible while listening to music? I'm assuming the overall sound is what it's supposed to be. It will take some getting used to after 25 years of listening to the Sunfire. Thanks.