First I'd go back to factory conditions. Then install only one game to try.
If there are still issues, you might have an issue that is covered by the warranty.
Since i bought my computer i've been experiencing some troubles with some apps. Mostly video games such as Half Life 2 and Source engine based games. The problem is that the game freezes and loops the last sound for, say 2-5 seconds. This is very annoying in more competitive games like DotA2. Actually, the problem isn't exclusive to Source engine games. I experienced it with MusicBee too, a music player application. With this, sometimes at the start of the track, around 20s, the music loops the last second the same way as with Source games. I think the problem occured with other applications but it has become so usual that i can't remember them. I never noticed any sound problems when using my computer with Linux-based OS but I can't be sure of its absence.
I tried updating and using every version of the drivers i could find, and the problem isn't about the device receiving the sound, i had this problem both with my headphones and my speakers.
The computer: http://www.digitalversus.com/laptop/medion-akoya-extreme-x7811-md-97589-p10236/test.html#full-review
It had a good performance/price ratio when i bought it, but this problem just ruins my gaming experience.
Thanks for helping!