Blown voice coil?

I am experiencing some really weird noise from one of my subs, it has just started recently.  I have two fosgate punch hx2s, wired up to a 1001bd, wired up for a 2ohm load, which makes them each recieve 500 watts rms, fairly common setup, it is all perfect match pretty much.  I have had these in my car in some boxes that I built for like 6 months or so now, when I installed them my friend tuned them for me since he has a very good ear for it (works at a shop, much more experience, I have no shame in saying hes better than me), so he set my gain and crossovers.  Well a few weeks ago I was thinking, wow I never reset them after my subs broke in, because for some reason these subs took like weeks to really fully break in.  So I turned up the gain and tuned it all myself, a couple of weeks later I noticed that on sub sounded really distorted.  It was getting bad, so I unplugged it and took the meter to it assuming it was a blown voice coil.  Ive had it out for a while, and tonight I was thinking about how strange it seemed that one would be blown so badly and the other would be absolutely perfect, so I hooked it all back up and metered it from the amp, figuring maybe I did the math wrong, I was right, I checked it and it all read out at 2 ohms.  Now I could just be being stupid and the ohm rating doesnt mean anything about it being blown, but I thought it would be directly related to it.  So what are other things that could be going on, it sounds like it could have possibly just blown a gap into the box and is letting some air in, but what do you guys think it could be?