I had the same problem with my GP not too long ago. It started with the faint lock sound then eventually just all together quit working. How old is your GP? The horns may be starting to go (sounds like they're pretty much gone). Check fuses first, then check for shorts in wiring but if they're all good then it's probably the horns. The horns start to corrode and the mechanical internals freeze up. I had a hell of a time trying to find horns for a decent price that were OEM (or at least sounded OEM). I finally found some on amazon for about $30 a pop.
