Hey ximrich,
I'm sorry you're running into this sound issue. I'll need to know a little more about the versions you're using currently in Windows.
First, your BIOS version can be found by pressing FN + ESC. Look for 'F.##' and let me know what that is.
Then, your IDT driver version. (Windows key + X > Device Manager > Sound, video and game controllers > IDT HD Audio > Driver tab) Let me know the version number shown there.
Have you tried any other BIOS versions than the one you're on currently? Have you tried disabling 3D Drive Guard?
Here are the steps to disable 3D DriveGuard:
1. Press the Windows Key + Q
2. Type 'hp'
3. Click on HP Mobility Center
4. Click on 3D DriveGuard. Click Yes to allow it to make changes.
5. Click the 'Disable' button next to HP 3D DriveGuard
6. Click Apply and restart if prompted to do so.
After the Restart, test your sound and let me know the results when you get a chance :)