I got a call the day before yesterday. Somebody told a phone system client that I can fix anything. They have had noise on their phone system since a major power failure several months ago.
They'd had another company look at their phones who just told them they need a new phone system. They might, but I don't think so.
I took a look yesterday, and I probably told them how to fix their problem without me.
They have AC circuit line noise. Something on the same circuit as their phone system probably started making more noise on the line after that power failure, and the marginal conditions surrounding it. Also, somebody added a clean air machine in the office where the KSU is, and whenever the fan for it kicks on their phone system noise increases.
Now maybe their power supply could have filtered most of that noise except the AC to the KSU is a piece of romex coming out of the floor bundled with the incoming phone wires and the outgoing extension wires.
They pretty much guaranteed that any excess noise on that line will be induced onto their phone lines and extension lines. Sigh. I don't know how they ever didn't have noise, but the first thing they needed to do was disconnect that piece of romex, find anyplace else (like the ceiling between floors) its parallel or bundled with and disconnect and abandon that part, and run a new dedicated circuit IN CONDUIT from the breaker panel to then outlets here the KSU is plugged in.
What I got was, "Well maybe I can run an extension cord from somewhere else."
Sigh, if they got anything I said all I did was troubleshoot their problem for them for free. Sigh. I don't think I'll go back if they call again. I knew it was going to be one of those calls just from the phone conversation before I ever went though.
Some things you can't fix... phone systems isn't one of them.