I would say hearing a "crunch" when wrenching on a CF bike in the least, is nothing to ignore. Only the OP can make a good enough diagnosis by dismantling the front end of the bike and track down the sourch of the crunching sound....then take a pic and maybe show us all so maybe someone here can be knowledgable enough to examine the pic and forward an opinion......that's all.....
As for the invincibility of Aluminum forks, I would not think it's the "end all" for assuring a problem free front end forever......I think you have better chances getting that with Steel or Ti forks.
JMOs
Chombi