Not a musical joke, but I shot milk out of my nose when I heard this one...
===========================================
A fire fighter is working on the engine outside the station when he notices a little girl next door in a little red wagon with little ladders hanging off the sides and a garden hose tightly coiled in the middle.
The girl is wearing a fire fighters helmet. The wagon is being pulled by her dog and her cat. The fire fighter walked over to take a closer look.
That sure is a nice fire truck, the fire fighter says with admiration.
Thanks the girl says The fire-fighter looks a little closer and notices the girl has tied the wagon to her dogs collar and to the cats testicles.
Little Partner, the fire fighter says, I dont want to tell you how to run your rig, but if you were to tie that rope around the cats collar too, I think you could go faster.
The little girl replies thoughtfully, Youre probably right, but then I wouldnt have a siren.