If you read the riddle out loud, then it’s that sentence. See, it ends with the words “a drop,” and the sound goes 600+ mph.
Sound stops with a drop in volume, so my bet is Philster has the best answer. Though Maglev trains are good, I’m not sure any in service go 600mph yet, and don’t necessarily drop to the track when stopping do they?
Let us not forget the speed of sound which, according to Google, is 761.207051 mph at sea level. That is 161 mph over the OP.
Yeah, but DJs aren’t exactly Alfred Einsyein.
And Zebras don’t notice the OP says over 600 mph which 761.2 definately is 
A duck!
Dammit, he always wins!
And who art thou, so skilled in matters scientific?
Viaduct?
But after the drop, it doesn’t echo, and no one knows why!
A waterfall? Angel Falls maybe?
That’s my vote so far.
Sitting right on the Equator, approximately 600 miles directly west of Ecuador, are the Galapagos Islands. On the largest island can be found the poor village of San Del Sando. The villagers get their drinking water from a single rusting water spigot located in the middle of town. The water from this spigot (like every thing else on the surface near the equator) circles the axis of the earth at the rate of about 600 miles per hour.
The cutoff valve of this faucet is not well seated. When it is turned off it drips… until, at last, a final drop drips.
Things on the equator circle the axis of the earth at something over 1000 mph (the earth is about 25,000 miles around, and rotates once per 24 hours).
supermans orgasm
Declan
I think you’ll find that comes out at a little less than 30mph (hey, He ain’t *THAT * super) … and once it’s stopped hurtling will swim ovarywards at 0.11mph
So right you really are, Joe, so even better, lets move the little village of the Galapagos to the latitude of Philadelphia, or maybe to Baltimore.
Think about it, we can exact the terminolgy of the quiz by moving our hypothetical leaking fountain a few miles towards the preferred answer.
Offbeat, but…
A mechanical squeak? As a sound, it travels over 600 mph, but stops with a drop of oil.
Not good enough?
A cup of Maxwell House coffee in coach travels 600+mph and is good to the last drop.
Organ music travels 600+mph and drops with a stop.
If my pants were on fire, I’d do my best to exceed 600 mph, then stop, drop and roll.
Electricity, considering that electricity travels almost at the speed of light, and light defenitely travels over 600 mph. And, electricity ‘stops in a drop.’ if a drop of water spilled onto it the electricity would short-circuit [stop] and therefore ‘stop in a drop.’ so, electricity is my answer.