KX155 trouble.

[Lood]

I bought a used KX155 from a US avionics company about two years ago and have had continious trouble with it since day one. It makes a static or scratching noise, to such an extent that it all but useable. The avionics shop at my AME has had it on their bench many, many times and everytime we're sure that the problem is solved. Unfortunately, it only last one or two flights before starting again.
At times, I have thought that it might not be the radio but rather something to do with the wiring or antenna or maybe the installation, but everytime they put the radio on their test bench, it also makes the same noise there. They've tinkered with settings, replaced small electroninc components inside, etc. but the problem just won't go away. Interestingly, the radio can sometimes function 100% for a complete flight, just to return to ops normal with its noise on the next flight.
Is radio a dud and should I just chuck it away and get another? Seeing that KX155's are still very expensive, I've even thought about replacing it with another KY197 together with a KN53 for the nav part?

[jetdriven]

By the time you rewire and mount the cans, those other radios would have to be near free to make it worthwhile.  What about the audio panel? Borrow a friend's 155 and see if its your plane or the radio?