I've got a really annoying crackle coming through on one of my monitors on bassier sounds..... But cant see any damage to the bass speaker/cone.
Could something like that be cause by a dodgy mixer and cable connections (im using my housemates mixer to run my controller through and its a pretty knackered piece of kit).
Could be bass port turbulent noise? On my monitors I get some turbulent noise that is a bit annoying, but is generally unnoticeable when there's plenty of mid/ high content to mask it. But it doesn't sound like a crackle though... crackle suggests some damage or fault in the signal path, possibly overloading somewhere.