help concerning a car audio cd radio receiver

lately the radio receiver started to deliver low quality signal when set to the fm band , the audio drive is JVC , when the car is static , the quality is rahter nice , but as soon as the car moves , the signla goes very bad ?
what can cause that ?

There are many possibilities.

Maybe something else in the car creating interference.
Try a portable radio in the car and see if you have the same problem.

Maybe the antenna cable is broken or there is a preamp at the antenna that is not getting power.

thats true , i have another classic radio casette drive and its radio is working pretty fine , so i think its not the antenna cable nor the preamp .
yesterday i noticed that it depends of the nature of the place , if there are many buildings , the signal gets very poor .
Any suggestions , what can cause that in an fm receiver ?