Well, now there's a good question BB,...i'll have to give that some thought??? Really, never considered it even,...but you said "song",...does it have lirics? The only thing that comes to my small mind, is the lead up to the Kentuckey Derby...Oh wait! you might mean the "William Tell Oviture"...:)
dut dida dut didda dut dut dut, dut dida dut dida dut dut dut...yeah, I think thats it...
hope that helps...
Yeah, I finally found it after I posted this...William Tell Overture - found a pretty cool cartoon on YouTube he liked pretty good.
http://www.youtube.com/watch?v=IErXg5kBXXg
I'm happy I could help 
Noah really likes it when we put him on our knee and "ride the horsey" - he really likes it when he hits a "bump" - I hoist him in the air and rock him back and forth on his way back down. He laughs and smiles, it is a lot of fun.
What is the name of that classical music song they play at horse races? I want to find it on YouTube, we pretend like our son is riding horsey, and I would like to play the music in the background...