Yours is a clear case of relapse. Why the relapse happened is a matter of discussion. Also, you seem to be having a condition called BRUXISM, wherein there are symptoms similar to what you have mentioned.
Next Steps
Relapse can be corrected by doing Orthodontic Treatment once again. Make sure you prevent relapse again. Bruxism or not, crackling noises are to be sorted out. You need to get it checked for issues. Please do not ignore.