Windows 7: Different sound output with different headset

Cheers all,
Been trying to search for anyone with this similar problem but no luck so far.

Using windows 7, 64bit.

The problem is the sound output, when I use my sennheiser headset with microphone, plugged in as usual. pink to pink, green to green. I get perfect sound in a game and listening to music. However, some aplications such as teamspeak and voip-application makes the sound very very low.
I can use the game and teamspeak at the same time and get perfect sound from the game.

When I change to another headset (noname, uncomfortable) everything works as it should. The sound is ok in all programs and the sound levels are good.

I do not change anything in the settings, no change to volume settings on the headset cables and they are plugged in the realtek mobo card the exact same way.
All volume settings in the windows volume mixer are set to max for all applications at all time.

Drivers are updated.