It's a high side driver, so the switching pin either conducts to ground or floats. I think the LED- node isn't exactly floating as the inductor is supplying current once the switch node floats.
Wouldn't a voltage spike directly translate to a current spike anyway? Especially for a diode where a small change in voltage causes a large change in current.
Since the intent of this is to drive an LED load, I used a zener diode which behaves roughly like an LED.
In my board layout, I was careful to keep all important traces very short. The long traces are in the cables that attach the load.
**broken link removed**
I agree that the spikes probably won't hurt the LED, but I'd like to know why this is occurring. Or perhaps it happens in a lot of LED drivers and people just haven't noticed because they weren't using 200+ MHz scopes?