I have a trouble call coming up and not sure what to look for. The customer says he had a new air cond system installed, a split system with a variable speed indoor blower unit. Now every time the unit starts, his flatscreen TV goes nuts with buzzing and lines on the picture. It didn't happen before the new AC was installed. The TV is NOT on the same circuit as the AC. The AC people came out and checked everything and said there is nothing wrong with their installation. The new AC replaced an old one that was in the same place, on the same circuit, and didn't cause any interference on the TV.
I can't think of anything except putting each on opposite legs of the service, if not already done, or installing a filter on the TV. (The TV is built in so he has not tried other circuits using an extension cord.)
What else can I look for, or will it be a total waste of time?