I was going to see my doc about this by I thought I would throw it out there.
I have been getting a pretty significant pop in my right inside knee, actually since starting the front split series a few months ago. Sometimes it comes with pain, usually when my knee is fully bent. Pushing my feet in during butterflies hurt the most.
I don't notice it in most of my daily activities. In GST I feel it in deck squats unless I get it just right. I've decided to go back to the regular squat and work on foot position there.
Any thoughts or experiences with this?