If this is windows CE and it give you access to it when updating, why wouldn't you be able to find that sound file and delete it.... better yet just rename or move it to a different folder...
Now that's the kind of suggestion I was looking for!
Thanks thegeck! 
(Though, like my last head unit, Pioneer should just let you turn the damn thing off) 
Also, I thank everyone for weighing in but am finding it interesting that some people don't mind the unit beeping every friggin time you touch it, where others do. I'm obviously in the latter category. And I admit it annoys the crap out of me.
As I mentioned before, I've been designing touch screen interfaces for over 10 years. Button sounds were all the rage when people first started designing them "wouldn't it be cool if the computer made a sound when you touched a button?...Yeah!" Well after years of development it turns out people (usually) weary of them quickly. Took me only a month or two of debugging early prototypes...beep...beep...beep...and so on. Properly designed and coded touch screen programs should respond by doing what they're asked to do.
I ask everyone to consider, do we expect the other controls in our car to beep? Or the levers buttons and knobs on our home stereo? Or the "Back" button on your browser? I could go on but you get the point. We've been conditioned to think beeps on a touch screen are normal when actually they're a vestige of a failed experiment.
Obviously you can see I care about this
But to each his own. Again, I appreciate hearing from everyone.
Beep 