My knee makes a loud crunching noise when hiking uphill; minor achyness above the knee after a long hike. pretty hard fall 3-4 years ago. what's up?

Patellofemoral pain: Sounds like patellofemoral pain syndrome. You could try nsaids, quadriceps (vmo) strengthening with terminal knee extension exercises and hamstring stretching.

Chondromalacia: Most likely you have chondromalacia which is a wearing of the back of your kneecap. It could have been from your fall. Try nsaids and maybe a joint supplement. If no improvement get it checked out.