I think it is a shifter cable problem. Mine does the same thing, and I asked the dealer to adjust the cable at first service. It's getting worse, so I assume the cable is stretching and needs to be adjusted again. It sure is an ugly sound when it pops out, so I DON'T mess around when I put it in L, I put it in hard, and give it a little backslap to make sure it's in. I just ran out to verify what I'm saying before I embarrass myself, and it looks like it can be adusted at the shifter or the tranny. I can't see it very well, so just check the manual.