Hello, I have no idea why when doing single leg circles or opening my hips I get a grinding sensation and a noise!
I am a runner , thinking I need to work on the hip flexors?
Any tips. It feels odd.

Go through the movement really slowly and find where the clicking happens then see what your body has to do to make the femur glide smoothly through the socket. Once you have the action down you can pick up the pace a bit. Usually you have to start by making the circle smaller and extend the leg out more where it clicks. Hip stretches can help here as well. Play around with stretching the outer hip and hip flexors. Do one stretch at a time then try the movement to see what stretch help and then you can see what area of the body needs focus.

Amanda, thanks so much for your advice will try this.
Playing around and smaller circles may be the key! Yes I have tight hip flexors. Cheers.

I do this too.. I think its something in my pelvis but I havent figured it out yet.. i notice it during leg circles and a few other exercises with rotation of the legs . Its very loud and its getting worse.. also its a bit uncomfortable.. I notice if I either add small ankle weights or do circles with legs in straps on the reformer its not as bad.. I wish I could figure this out!!! If u figure yours out let me know..

Me too. I have also developed a sore butt! My greater trochanter is tender and now a small patch of skin just beside my trochanter has gone numb. Even the doctor thinks this is weird. I have normal hip movement if I keep my leg straight during leg circles but if I do a lateral rotation I am a clickety Ann! I also started to begin this exercise with the lateral leg stretches to confirm my range of motion,and stabilise my hips.

I agree with Amanda, try to do smaller circles and you will see everything goes better. It may happen when you do similar excercses in the reformer, let us know, if this advice works for you.

Possibly it is your SI joint making that noise? That is quite common with leg circles.

I used to have the same problem...it's called "dancer's hip" you can google it. It's a tendon flipping over the trochanter in most cases. I started working on strengthening my glutes and hamstring connection so that i gripped less in my hip flexors and the problem has mostly gone away. Hope this helps!

Something that has helped me immensely has been to change the intention of the circle. Meaning....instead of reaching out and 'drawing a circle on the ceiling', I visualize the circle happening in the hip joint itself and brining the femur head into my body. I anchor like crazy (I"m a bit hyper-mobile in the clicky hip side of my pelvis), pull the femur in and back to the mat. My teacher, Pat Guyton, helped me with this. "Amy, imagine you're making the circle on the mat behind your hip joint, not in the air and make the circle smaller.....feel the circle---don't draw a circle". This is the one thing that has helped me. Maybe give this a try too!

Such good tips for this.. Erin, I really think thats my prob..cause it always creates such a loud pop and i can feel that sensation of something in there not connecting correctly no matter how I change positions or try to make smaller circles.
With my knee issues and my SI issues I think its making sense to me to try now and strengthen those hammies and glutes..Gonna try it!! I supposed to be doing that anyway to help recover this knee.. Thanks