I haven't had any luck troubleshooting yet, kevs, but I've adjusted my sound pref like so, and although I can still hear the sounds I want to hear, e.g. move to trash and empty trash, the unwanted sounds aren't near as objectionable.

So far, I've tried trashing Microsoft AutoUpdate and NoSleep, which is responsible for the only 3rd party kext I've got, but with no joy. I guess I"ll have to go through my launch daemons and see if I get lucky.

Have you got any of these guys in /Library/LaunchDaemons?

com.apple.installer.osmessagetracing.plist
com.bombich.ccchelper.plist
com.charlessoft.pacifist.helper.plist
com.daisydiskapp.DaisyDiskStandAlone.AdminHelper.plist
com.microsoft.autoupdate.helper.plist
com.microsoft.office.licensingV2.helper.plist
com.rogueamoeba.aceagent.plist

The new Great Equalizer is the SEND button.

In Memory of Harv: Those who can make you believe absurdities can make you commit atrocities. ~Voltaire