get a new cassette and that will help alot with the crunching...at least mine did when I put on my sram 990 and check your bottom bracket for the creaking. I noticed when I was washing my bike that a little bit of water here and there was getting down my seat tube and ending up at my bottom bracket since it has nowhere else to go. the creaking can then come from sand/dirt mixing with that water at the BB creating a creaking sound....might not be the reason, but just a thought