Why does car radio cut in and out?Only does it while listening to radio, but does fine with cds.?

Question

01 Pontiac Aztek 6 disk stock radio with 6 stock speakers with steering wheel radio controls + rear controls.

Also has controls in middle so back passangers can listen to either the cd or radio while the driver listens to the other.

Only does it while listening to radio, but does fine with cds

Wires at outside antana seem to be in place. so could be something in dash or something with all of the contols or the radio its self. Any help would be of Great. Thank you

P.S

put your self in my position your singing a song then someone cuts the volume and then turns it right back up.

Thank You

Answer 1

Something gets in the way of the signal.  Ex.  Going under an overpass.  The concrete cuts the signal, so the signal from the satelitte does noot reach your car.

Answer 2

Bad Antenna.