Source: http://support.apple.com/kb/ts2771
- Check the volume setting on your iPod touch. You can adjust the volume by pressing the Volume Up and Volume Down buttons.
If the issue appears only with content created using the microphone (located on the back next to the main camera or near the Sleep/Wake button), make sure that nothing is blocking the microphone.
- If you are using a protective case or film on the display, make sure it is not covering the speaker or microphone, or completely remove the protective case or film.
- If the device is in a dock, remove it from the dock.
- Check that the speaker opening is not clogged with lint or other debris.
- If the speaker or microphone opening appears to be clogged, use a clean, small, dry, soft-bristled brush to clean it.
- Use the brush to carefully and gently brush the speaker and microphone.
- Brush away from the Dock Connector to avoid getting any debris into the connector.
Contact Apple Support.
Locate a Service location: https://locate.apple.com (choose your country in the top right)
Call Apple for Mail-in Service (if available): http://support.apple.com/kb/he57
Set up service on your own or check options: https://selfsolve.apple.com
Questions about service and potential costs: http://www.apple.com/support/service/ (Choose your country after selecting your product)