2010 Fusion FM reception
 

I recently bought a used Fusion and am having a problem with the FM reception. The highs come and go frequently, kind of like switching from stereo to mono and back. The ST light on the face never changes. I went back to the dealer and they sent the radio in for repair but no problem was found. I drove another Fusion and I think it did the same thing but it was a hurried test. Does anyone have any info on this? Thanks