when I am on my cell phone in my 2013 Legacy and I turn on the head lights the person on the other end hears a loud buzzing noise like a horn blaring or something. If I turn off the Head lights the noise stops. I want to install a ferrite noise suppressor on the headlight ballast but I don't know where to find the headlight ballast. Please help.

So, I'm assuming your car has HID headlights then? Usually a halogen wont causes those issues.

 

Ferrite coils might work, or it might not. All depends what kind of interference that's happening.

 

Interference can be because of the magnetic field,which, gets fixed by the ferrite coils.

 

Or it can be the ballast is emitting it's own waves which happen to be on a similar frequency as the Bluetooth.

 

Then lastly, the interference can be getting into the Bluetooth equipment via the 12v power wire.

 

I'm having a similar problem with interference on radio waves with my LED headlights.

 

The ballast should be a box that's either directly next to the bulb (in the lens) or more commonly, near the lens on the frame rails.

So the other person on the phone hears the noise, but you don't hear anything?

Do you still have the factory radio or is it aftermarket? If it's aftermarket is the reciever/microphone wiring run anywhere near the wiring for the headlamp switch?