Originally Posted by SargeW
Are you sure it's not the hydraulic jacks warning buzzer? Stiff bumps can wiggle a loose jack as well.
The jack(s) down warning light is in a different place (a single light low on the dash, not on the multi-display), and the warning sound is different (repeating, different frequency, not a single loud buzz), on our '06. If it's the same on the '08, that would make it difficult to mistake one for the other.
If the air pressure is normal, I'm with Lt. Dan on this one. Without knowing the details of the wiring, I'd look at the connections at the parking brake button and the low air pressure warning switch in addition to the one he suggested if the latter isn't the problem.