Door Speaker Issue - Blown?

I started the C63 this morning and all of a sudden the door speaker from the front passenger foot-well sounds very distorted with any bass notes. I can keep the volume low enough that it is not noticeable, but if I turn the volume up just a little more (I wish we had a numerical reference for this in our stereos), the speaker sounds distorted. There is almost no chance that I blew the speaker as I never listen to loud music. I am wondering if anyone else has had this happen? All of the other speakers are fine.
Could it be caused by opening and closing the door ( I have the coupe)?
Could it be due to low voltage?
Has anyone replaced a single speaker due to this issue and was able to resolve it? I searched on here and did not find much info. All help and insight would be appreciated (just so long as you aren't suggesting to listen to the tailpipes, I fully understand that concept).
Thanks,
J





However, with a cheap little rivet gun, why bother going through all that, just pop the rivet in, clamp, and done!


