An oscilloscope probe has capacitance between the probe tip and ground
connection. Any inductance in series with this path makes a resoant
circuit that rings when hit by a fast transition. I highly recommend
reading Tek's "ABCs of Probes", which you can get at

http://www.tek.com/Measurement/App_N...60W_6053_7.pdf

It mentions the phenomenon on p. 10, but it would be very worthwhile to
read the whole thing.

Roy Lewallen, W7EL

Paul Burridge wrote:
. . .
The short prods inplace of the flying ground clip certainly reduced
the ringing quite considerably. I'd be interested to know why a long
ground lead is a Bad Thing...
. . .