I am updating because the hum is now in both rears (it always had been) but on different drivers. so on the left speaker it is the upper driver and on the right it is the lower driver. It is in both tweeters. If NOT the 7500, could my speakers be showing blown crossovers? Because the bottom line is that the 2200's are not producing a hum and the fronts now are free of hum. The process of elimination is starting to point in the direction of the 7500.