If you are sure its your crank than the most likely culprit is the interface between the BB axle and the crank arm.

A crack is possible, but pretty low on the likelyhood. Professional mechanics that have been in it for 30 years still use the process of fixing one thing, checking, fixing the next, etc. Because it is so hard to diagnose the exact location based soley on a sound. There is just so much going on in that area. And lots of problems feel very very similar/ the exact same.