If you have not done so, try restarting the iPad. Hold down the power button until you get the red power off slider. Once it is completely shut down, hold down the power button gain for a couple seconds. I've found this often clears up odd sound behavior.
Also, under Settings > General > Sounds you will see a switch just under the volume slider. If this is on your Alerts and general volume levels are always the same. I like to leave it off, with the slider mid-range, so that my Alert volume does not change with whatever else I'm doing.