Sue, that is one of the problems when creating a narration with PowerPoint
unless you have a very good noise canceling microphone.  What some people
do, believe it or not, is to take the monitor, mouse and microphone into
another room (with extension cables) with a closed door between them and the
computer and do the recording away from the computer's whine.  Most
professional training presentations are done with the narrator in a
soundproof room with only a monitor and microphone.

Of course the first step would be to turn off all the mouse click effects
that is turned on with the normal Windows setup.