Swanie licking his tail - shoudl I be concerned

For the past couple weeks, Swanie has been licking at the bottom of his tail or sometimes on the white part of his fur under his tail. I've had him to the vet twice, she's checked him and done a urinalysis and basically doesn't know why he would be doing this. He doesn't seem to be in pain and is behaving pretty much normally other than this behavior. I took a couple pictures of him doing it this morning. Does anyone have any ideas about why he's suddenly doing this? Should I take him back to the vet for another look?

(For some reason I can't upload photos from Photobucket, so I had to do it from my computer).

Do you mean that he's doing this excessively? My cat regularly does this when she's cleaning herself.

Originally Posted by Devanagara

Do you mean that he's doing this excessively? My cat regularly does this when she's cleaning herself.

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yes, he's doing it excessively, and not really in conjunction with a general cleaning of himself. It's definitely unusual behavior for him. I've tried touching his tail and around that area to see if he has any pain, but he doesn't react as if he does.