Looks like a bad sensor, but I suppose a bad cable could cause it as well.It happens everywhere, not only in a garage and it's a permanent issue, it happens all the time.
I don't think that it's an interference in a cable going to the rear camera. I use a standard cable that was sold with the camera. It doesn't have any chokes and I didn't add any as when I installed the camera everything was OK. Why would it interfere now? I haven't re-routed the cable.