There is no way to adjust the volume. You can adjust it to flash 3/5/7 times in one of the menu settings when you give it a quick pull and release. I believe the default is 3. I changed mine to 5 because it is the perfect length of time for me when changing lanes or taking an exit ramp.
As for my opinion of the volume, I've never considered whether the volume was too loud prior to reading this post. It has never bothered me.