You get a tuner for free. What's wrong with that?
The problem is it's not a tuner. A tuner let's you, uh, tune to the frequency you want. Something they used to teach everyone back in the 50's, before education got so dumbed down nobody knows anything any more but false facts and jokes. Oh well.
I am not kidding. Common grade school project was to build a crystal radio. So as a little kid we learned about radio waves being everywhere, picked up by every wire. The trick is to tune to the frequency of the radio broadcast you want to hear. So OP does not get a tuner for free. But he does have something in there that is doing the tuning for him. The solution is to find it and either make it stop or eliminate the source getting to it in the first place.
This really is no different than what happens all the time with phono inputs. It's not uncommon to hear radio broadcasts come in frighteningly clear. This also shows how in spite of what so many guys think RFI is everywhere, all the time. Usually it is sort of like a uniform white noise that no one really notices at all until we do something to reduce it. Then it's crazy how big the improvement can be.
Okay that should be enough to guide you to finding the problem- its just like tracking down any other source of noise.
