No sound after joining Do

Hi,

perhaps someone can help me. I installed Vista Business on a HP6730b.
Sound worked fine until I joined our company domain. The devices are
shown in the device manager without errors. If I test the speakes I get
a message that the test tone can't be played.

A retry brought the result. If I do a recovery to state before the
domain join, everything works fine.

There are only some basic GPO's applied, like Windows Update but without
any restrictions for services or devices.

Has anyone an idea what I can try to get the sound working?

TIA,
Daniel