merry christmas everyone dedicated lines..????

hello. i have 2 dedicated lines, one for the tv and one for audio. i am having some difficulty with my AC. i'm trying to address a ground loop hum due to my cable service. however that is not my question today. how it possible, with dedicated lines, that if my wife uses a hairblower in a bathroom three floors up i get hum bars across my t.v. and a terrible buzz through my stereo. i suspect the lines are not actually dedicated. any insight would be greatly appreciated. thanks, d.