m4600 - multiple modes for headphone jack?

Hi,

I have a bit of an issue with my m4600. When I am plugged in with my headphones I hear this annoying micro-beep sporadically. Quite often it coincides with a mouse click or screen change - but not always. Its very short, and sounds like a static, interference, ground loop type noise rather than and actual sound file being played.

A couple of things I've noticed.

1. It doesn't happen through the regular laptop speakers. If I unplug the headphones, I don't hear it.

2. If I am playing something, then it doesn't happen. Certainly watching youtube and bbc iplayer surpresses the beep. This isn't the beep being downed out, it just doesn't happen. I would assume i could technically play a silent mp3 file constantly and the problem would be resolved. Not ideal though

3. The headphone volume seems very high. When I have my standard 'bud' earphones in, I only have the volume on the bottom, second bottom or third bottom settings. Having the volume half way up is totally deafening.

I'm wondering firstly if this is a "problem" endemic with all m4600s that I should accept, or whether there is an issue with my system that I should try and get resolved.

Although my system was delivered in this state, I'm also wondering if there is a configuration issue that I'm missing? Some sort of sound boost, or seperate headphone mode? I noticed that when I accidentally put the headpone jack into the adjacent microphone jack, a menu popped up asking my to select the usage of the port e.g. line level/mic/etc. Is there anything similar for the headphone jack?

I also note that I seem to have two sound devices - both attached to the "IDT High Definition Audio Codec"

- Speakers/Headphones
- Communications headphones

What is the difference between these two? I only have one headphone jack and I don't see any other way to connect to the IDT device.

Any thoughts appreciated. Thanks