No sensor on the 07....doesn't have anti-lock brakes.
I got it to do it after parking it on the back patio.
I had just finished riding and pulled up ...went to dis-mount and heard it click.
Was able to rock the wheel back and forth and put my hand on it to try and locate it.
Feels like it's in the left brake caliper...Do you think it's a pad sticking possibly?
I know it's nothing to be alarmed about but it's annoying!
I was gonna suggest looking at the calipers, before reading your response...now that I have read it, I would say that you SHOULD BE alarmed if you think it is a pad that is sticking...thats gonna cause the rotor to overheat and warp - if it hasnt already. Warp it far enough, and it might lock your front wheel, causing you to fly over the handlebars.
I had a similar issue with my 03 Z. Turned out that the pin that holds the pads in place had a slight raised edge where brake dust had built up on it, and the pads were hanging up on it. Surprisingly, a little bit of rough sand paper took it right off - but I still had to pay $200 for a new set of rotors off eBay, since the left rotor was warped like hell...
Good luck bro. Take care of it post haste!