As a therapist and cyclist (recreational only) I have also experienced this. I would suggest seeing some one whether it be an acupuncturist/ deep tissue therapist or even a sports physio to release the tight muscles on the outside of your leg. When you get a knee problem like this which sounds like patellofemoral pain syndrome it helps to get it treated. I had my chinese acupuncturist needle my patella tendon which sounds painful bu really helped but wouldn't really recommend it if you are not comfortable as it is quite an aggressive treatment. This will help you have a chance to strengthen your muscles with exercises such as squats which are nice and safe and smash some stretches for your gluteals and quadriceps.
Gluteal Stretch in Lying - YouTube gluteal stretch
If you are keen lie on a tennis ball to release your outside thigh muscle and your gluteals as these are muscle most likely to be tight.
I was wondering is there a reason it may be one sided i.e. previous injury on that side?
Also it doesn't harm to adjust your bike set up slightly ie raising seat height or pushing seat back just a tiny weeny bit but feel free to consult your bike fit person.
Hope that helps.