Thank you for your answer Lars. I checked my BIOS settings and my CPU (Phenom II X3 720) was running at the normal 2.8GHz. I underclocked it to 2.7GHz, disabled AMD C1E and activated HPET. I don't know which of the modifications helped but until now I did not experience any problems. At last I can listen to music again under ubuntu :)
Thank you for your answer Lars. I checked my BIOS settings and my CPU (Phenom II X3 720) was running at the normal 2.8GHz. I underclocked it to 2.7GHz, disabled AMD C1E and activated HPET. I don't know which of the modifications helped but until now I did not experience any problems. At last I can listen to music again under ubuntu :)