It can be caused by several things one being corrosion by trapped moisture. I run the Gulf in the fall and the salt spray can find it's way back behind the leading edge. I had it happen on a NGQ WInglet it is not entirely uncommon.
Sensenich should be contacted and allowed to inspect the blades and what is left of the leading edge if you still have it. Mine was an easy fix. If the blades are noy newer it may be a good opportunity to get them refinished and balanced too.
When my winglet lost its bond it did so on one edge first. I'm out in the swamp with Trucker Mike and hear "knock...knock...knock" at low rpm. I rev it up and it goes away, bring it back to idle and "knock...knock...knock" like a rod knocking. We are both like WTF, we limp it to a pull out and are thinking what are we gonna do to get back to camp when I noticed the flapping leading edge. Got on the phone with Darrin at Sensenich and pulled it off, no more knocking sound. It was that leading edge clacking like a bad rod...lol