"Drags" and "buzzes" sound to me like a buffer problem. While this isn't necessarily part of Kontakt per se, it is sensitive to your free computer resources and perhaps Kontakt (combined with whatever software you've got going in the background) has used up enough resources that it's becoming hard to keep processing the buffer. This problem isn't uncommon in audio environments due to the desire for low latency times.
Since you're on AMD, I'm presuming you're running Windows, which means you're probably using some kind of ASIO driver for low-latency audio. Somewhere in that driver or in your recording software should be a setting called "Audio Buffer" or "ASIO Buffer" or something to that effect. Generally this number is a power of 2, although it doesn't strictly have to be.
Try raising this value. This is the number of audio samples kept buffered before they're sent out to the hardware. The higher this number, the higher the latency time (because of the larger buffer to fill) but the more resilient the system is to temporary losses of resources - if something else is tying up the CPU, you've got several milliseconds of buffer to burn through before you start getting audio interruptions.
