A few days ago, I reformatted my laptop and just reinstall Windows 7 with a disk, not with the HP partition (don't like all the software's you get with the laptop).
Around 2-3 months before, I did the same - reinstall the OS from a Windows 7 disk. In them 2 - 3 months, I had the same issue but fixed it by disabling all the Enhancements you can choose like Bass Boost, Virtual Surround, etc. (I had these ticked, thats when the problem started).
However, this time I do not have any Enhancements ticked and I'm still having the problem.
To say so myself, I think I would be more a driver problem than a jack port problem.
I will reinstall the audio drivers, let Windows updates reinstall them and maybe download the HP audio drivers and managers and see what happens from there.