2000 sienna rear speaker

I have 2000 XLE. Right rear speaker is making RRR-SSHH-RRR noise when radio/CD/tape power is switched on. It does not stop even I turn down the volume. I want to replace speaker. Could some one guide me about taking out the old speaker and putting a new one? It is 6 1/2 inches regular auto or is it special?
What is the chance that it is wiring and not the speaker is at fault?
Thanks