I have a set of Kenwood 4 way 6x9's, very good speakers for what I need. They are roughly around 4 years old, and I listen to them fairly loud but not loud enough to cause any harm. The other week while four wheeling I turned my stereo off so I could concentrate on what I'm doing, I left it off for the whole trip and part of the trip back. When I turned it back on one of my speakers started popping / crackling when ever it tries to play bass. The pop gets louder the louder the volume is. I know I had some dirt get past the grills and it was laying on the surface of the speaker (I have my speakers in boxs facing up). So when I got home I took some compressed air and cleaned out all of the dirt. It still does the popping, so I swapped the speakers to see if maybe it was the amp that was causing it, when I swapped the speakers the same speaker (differen't channel?? was plugged into the other output of the amp) would pop. So I know it's something with the speaker.. I looked for any kind of rips or tears or anything that looked abnormal and couldn't find anything. Does anyone have any ideas of what it might be, or at least stuff I should look for or try.