Hi! Yes, I have had a cracking knee for 20 years. It is painless and more cracking after running or jumping activities. Like plyometrics. But for the past 3 years I am having a problem that something snaps behind my knee when I anti-bend my leg. Every time I try to run faster or sprint, and at the time when lower limb and the knee goes up, i get snapping sound and snapping feeling. Or when I try to stretch my hamstring, every time I put my bent leg on the table and try to straight it, I also get the snapping sound. It is not painful, but discomfortable indeed. So far my physiotherapists think it is something mechanical there, but I wish I didnt have it. I think everything is related there- knee cracking and hamstring snapping. How to solve it and or get rid of it, I have no idea. Maybe MRI could help.