Magnet mount antenna's are one of the worst when it comes to RX and TX.  They tend to get a lot of interference and/or feedback.   Antenna's want a large flat ground plane below them.  ie., roof or hood.
If you don't want to have a standard CB Antenna then you might want to check out Firestick's AM/FM/CB adapter.  I'm sure it will be better then that magnet mount.