Stupid suggestion, but have you got a pump on the side of the frame?
My pump slipped down slightly and when i put was go down a hill and when i was peddling it was making a ticking, but a loud one. I thought the bottom bracket had gone and went to the LBS and he checked and it hadn't. I went off and it was still doing it and then i noticed the pump had slipped down slightly and the crank was hitting it.
Never told bike shop though.