Like everyone mentioned, probably your (ARB) Anti Reverse Bearing. Most of them don't go out, they usually need to be cleaned. Take it out, clean in lighter fluid, preferably ultrasonic cleaner. Once it is clean, let dry overnight to get any moisture out, and then lightly with a cotton swab, coat the inside needle bearings with thin oil. Do not over oil. If this all fails, get a new bearing and put it in. Make sure if you get a new bearing, to mention L.H or R.H crank.
"Practice, practice and more practice, and if you think you're good practice some more". circa 2006, Cadman