Yes it is a dynamic relationship between the medial fibres of iliacus muscle belly and the iliopsoas tendon.
In all people if you watch while you scan in the short axis of iliopsoas at the level of the iliopectineal eminence you will observe the following.
In neutral you will see the tendon on the bone and the MFI anterior to it
When you perform hip flexion and abduction the iliopsoas tendon leaves the bone and rotates around the MFI muscle belly until it sits on top of the muscle belly.
When you then perform hip extension and adduction back to the neutral position this relationship is reversed.
In some people the reversal does not go smoothly and some MFI muscle is trapped between the tendon and the iliopectineal eminence. When this trapped muscle is displaced the tendon snaps down on the iliopectineal eminence causing the snap.
It is a dynamic process.
You can actually scan easily while performing the dynamic movements as you are scanning above the groin crease.