My Vulcan seems to squeak (or chirp) occasionally, mainly while idling. It's driving me nuts because I can't find the source!
The good news is, there's nothing wrong with your motorcycle. Someone may have either applied a little too much torque or maybe too little when cinching down your motor mounts. That or there is just a very slight alignment problem with the rubber mounts. The fix is simple.
Loosen both of the large motor mount nuts and start the engine. Let it idle a minute then shut off and re-torque the bolts to the recommended 32 ft lbs. The squeak will be gone.