It's caused by the probe.
You should have a little spring thing in the probe bag.
If you pull the hook and ground clip wire off a probe (they both detach) you can put the spring on the end of the probe, like this:
If you have a ground point close enough to touch with the spring it will really reduce the ringing.
nb. To get the spring off (and on) twist it in the direction that opens up the spring. It will come off easily.