2005 Explorer Limited speakers

I just bought a Ltd. I adore it. However, I noticed today that the front passenger speaker was crackling. Has anyone experienced any problems with their speakers? I have the upgraded audio system with the 7 speakers. How would I know if I blew a speaker? How many watts would each speaker be?
I like my music loud, but no louder than what I listened to in my '99 XLT and it only had the two speakers. I drove it for 6 years - no blown speakers. I would think that a Ltd. would be even better. Or am I expecting too much?
Thanks!