I had this problem on my '01 it turned out to be a short in the turn signal wiring...stealership replaced it, but I am not sure of the price as it was a while ago. I would check the wiring, check where the connector plugs into the back of the socket for scorching, I think that's where mine was shorting, but again it was a while ago and I don't quite remember. Most likely a wiring issue though.
I have... 12 JK 4dr Sport 2.5" higher on 35" Rubber
I had... 05 Rubicon - Ssssssstock
I had... 01 TJ Sport - 4" Superlift, K&N FIPK, 31" Firestones MT's on Black Cragar Soft 8's, B&M Shifter, Rubicon Rocker Guards, Flowmaster Delta 40, Uniden CB