So I got 3 15 in dual 2s wired in series tuned to 33hz on an audiopipe 30001d amp isn't turned up a little under half no clipping and as normal subs gets a little warm never hot enough to where u can smell the coils burning up. Now my issue i ran into today Is I was listening to them going to lunch with no problems and shut the truck off and came back out and just turned system on and how I can describe it is one of the subs instantly started to make a distorted rattling noise... kinda sounds like the sub is farting all lower frequency but not noticeable at higher frequencys. I pulled speaker out and the coils dont have any noticeable scratching or rubbing.. Now I'm just stumbled on wat the issue could possibly be.? sub still works and hits just as hard as before but with a distorted rattle noise. Any help would be apappreciated thank you