do you have some aftermarket LEDs (i.e. interior lighting) installed?
i had issue with FM radio reception, and once I removed LEDs problems disappeared.
not sure why

 

No, I have the (original) halogen ligths. The problem doesn't change if I change my lighting settings too.

I know the issue although, LED's can make some high frequency distortion that can disturb FM broadcast. I know this problem in my house with cheap LED lights . .

 

Could be a problem with the cable between the antenna and tuner?

 

I use a CB radio when driving on the highway and place a magnet-mounted shortwave antenna on the roof for it. When I first started using this setup on my 2015 Mazda3, I ran the shortwave antenna's coax cable across the rear window and into the trunk. With the coax located there, my factory radio's AM and FM reception was drastically reduced, I suppose because the factory antenna is in the rear glass. So, I no long run the shortwave antenna's coax across the back window, and the factory radio has resumed its excellent reception.

This story doesn't seem to relate to your problem. I recite it only to show that the factory antenna is sensitive to a coax cable from a nearby auxiliary antenna even though the coax is not physically touching the factory's antenna.