I bike 16 miles a day up and down hills 5 days a week for a little over a month now. When I extend my knees they seem to grind and crack on as they track. I work a labours job lots of lifting and squating. Will be speaking with a sports medical doctor about my knees to see if i can continue my commutes to work or if I can make changes and tweak things so I don't regret riding a bike to work everyday.