why am I hearing electrical drain at shut off?

My dad is using a Classe Multi channel amp wich I bridged for 3 channel use, the left surround speaker has a not harmfully loud sound, but a sort of electrical drain sound at shut down that I can hear from 30 feet away, why is this in only one channel? Any ideas would be great, I am not feeling that this is a red flag fatal issue, but it shouldnt be happening...thanks Chad