You don't say where you are, but if in the states, give Proshow support a call. They are usually quite helpful. One thing you might try - in the directory your show is in, there are a number of files - showname.psh (which is your main show description file and what you create in Producer) and showname.pxc (this is a partially rendered sort of file with stuff in it that Producer uses when working with the show). That file can get corrupted with some very strange results. Try exiting Producer then delete the .pxc file for the show
(NOT the .psh file!!!) then re-open Producer and open your show. See if that changes anything - I have seen some very odd things when that pxc file gets trashed (if it is deleted, Producer just rebuilds it again - it will take a few minutes).
As for more information, the pdf users manual actually has pretty good info. The things that I know that can cause the volume to "dip" are things like video files where normally they cause the main audio track to lower while playing (there are options in the slide the video is on to adjust that). Volume control points are added to the main track to adjust the volume - often used when you have a short voice over attached to a slide for example or just for leveling as needed.
As for your comment "I don't like making public mistakes like this (ie with 40 people all hearing my 'Stuff-up')!" - that is the way life is - you can do something that saves everybody from sure disaster and nobody sees you, step on a loose shoe lace and trip and EVERYBODY is watching
mikey