It could be the sound settings in an app or two rather than the whole device settings. Try starting up the tablet in "Safe Mode". While you will have limited access in that mode, you will be able to check certain sounds. If the volume is louder when in this mode, then you have one or more apps that are the cause.
To get into "Safe Mode" please do the following.
1. First turn off the tablet.
2. Next press and hold "Power" until you see the manufacturers logo on the screen, then release the power button.
3. "Quickly" press "Volume Down" and hold it for few seconds until you see the message "Safe mode: ON" or something similar.
4. If you wanted disable it, simply repeat the steps above, and you should see "Safe Mode: OFF" rather than on.