Mine seems to sound about the same, but I can't say I've paid enough attention to it to be sure. It's loud enough that I notice it when I'm listening for it.
I've heard a few people complain about other sound/volume issues. The fix for those was to slide the sound to minimum, then back to maximum in Settings > Sounds. You could also try turning the Lock Sounds off for a while, then back on to see if that resets the volume.
If the Change with Buttons toggle is on, then the system sounds will change whenever you change volume settings elsewhere eon the iPad (buttons or general sliders). I generally leave this off, and have my slider on Sounds set near the max; so I know I'll always here alerts and notification (unless I turn on Mute).
That's all I can think of.