Radio sounds like my am transitor radio I got as a kid in the 60's ....speaker, amp,where should I start it has cassette with CD player and amp in trunk

 

Sorry no one has responded sooner, I myself was on holiday visiting family.
Your description is somewhat vague...is it just the radio that is making the noise or does it do it with the cassette/CD also?
Is your unit a premium Alpine sound (easiest diagnosis, do you have a speaker in the rear deck)? ...from your description it should be.
I'm betting its your bass (or facsimile thereof) collapsed....very common, as a matter of fact guaranteed it will happen. Under the rear deck, exposed to the sun, its inevitable.