mach stereo problem in 98 SHO

I have a problem with my right rear speaker. It is not playing at all and when I hook up a different speaker that I know works the cone just pops out and stays out. I am thinking that I have a bad channel in my factory amp. Please let me know if any one has had similar problems or have any idea what is causing it.

make sure the you wire the speaker in phase, and make sure the load (ohms) on the new speaker is the same as the old one.