As far as the hum is concerned---you'll have to determine where the hum is coming from. One of the things you can do--is take a phone(let's say extension 20)--unplug it from the wall jack---take it back to the KSU and plug it into the ext 20 port on the KSU. That will eliminate all of the wiring. If you still get a hum---then it's in your KSU or your phone---if you don't get a hum---then your wiring is picking up EF (electrical interference). If it's just a hum on the line--then it could be the line--or it could be a bad ground, or it could be imbalance in wiring for the C.O's--etc etc. You've got to to some detective work and eliminate hardware, wiring, jacks, and so forth. Good Luck