Just to make sure ... have tried pressing the dial button in while you are on the homescreen. This brings up the volume dialogue. If you have tried this ... forgive me .... I just wanted make sure.

When did this start happening? It likely due to a change in settings or software you recently installed.

Do you use a bluetooth headset? Sometimes there are some issues with connect / disconnect.

Do you use a wired headset? Some people have had the connector not disconnect correctly.

Sorry to shotgun the questions. Just want to narrow it down.

Rob.