In reply to sheffieldrunner92:
Don't panic.
Although it could be articular, it sounds more than possible that it's iliopsoas.
These 2 muscles flex the femur at the hip, or if the femur is fixed, flex the trunk as in a sit up. Snapping is felt in the groin with or without pain.
I had this with too much rowing.
Google some iliopsoas stretches, rest from the causative completely, massage the painful area deeply if able, see a physio in the first instance.