banging off the sub

jo, so have n exact psw 308 in 44 liters br case. if I turn a little louder, then some songs (only for 3 or 4 pieces) come on 1 or 2 make such a quick bang… (so for 2 seconds, so about 6-8 bangs or so) so from the sub, it is relatively loud, and for nen sub on any case high ^^ so you ort immediately what comes from. doesn’t sound healthy. and at the beginning I thought it was a spit or just a cable that burns through, so a bang like when a cable goes through burns (or as with the glow bulb when it burns at the turn on, only louder. ) however the sub still goes as before. is the sub at the place already overloaded? because it actually does not sound really warped at the place at… by the way, at 100 hz with (believe) 18 or 24 db/oktave separated, so as steep as it just went.