Do you have ASUI installed? If so, you could open the services section in asui-settings and see if any of the sound services aren't running but should be (checked). Incorrect start orders can cause services to fail to start and result in a reboot loop. The maemo-control-services app incorrectly starts services at 20 (any of them) after you toggle them off and back on.

Required services can't be unchecked so you could safely uncheck every service in asui-settings and see if a reboot without lifeguard works. Rechecking the services you want will restore them to the correct orders they were installed with.

If you don't have ASUI installed and don't want to use it then you could install it and use its service manager to revert back to systemui. That way you could continue using its service manager and its MCE settings interface without using ASUI.