Track interruping

Hi,
I have a MBP, mid 2009, C2D 2,53 GHz, 8 Gb Ram, with a SSD and a HDD: SSD for the system and applications (I run OSX El Capitan) and HDD (replaces the CD drive) for the music.
Traktor version 2.11.2
The problem encount (both on X1, Z1 or CDJs) is that sometimes the track playing interrupts for a second (sometimes...maybe once per night).
Does anyone have any idea about what possible issues can cause this problem?
The problem isn’t caused by processor or RAM. They are in low limits.
Thanks.

What buffer size are you running at? Try raising it. 512 is a sweet spot.

El Capitan was the only OS X which caused audio spikes on my mac. have you tried installing the Maverick?