It’s called bleed over. The strong FM signal is bleeding over to the sensitive phono section. As long as you don’t hear it when you are playing a record then don’t worry about it. BTW, I have the same problem with my separate tuner and phono preamp. It is so low that it is not worth worrying about!!
Used correctly "bleed over" means a strong signal on an adjacent frequency is "bleeding over" or leaking into the channel you’re listening to and has nothing to do with overload, intermodulation or intermediate frequency (IF) images but rather insufficient receiver selectivity to reject it.