Music hiccup at the start of the song

When I play Music from NAS or from local HDD I get an annoying hiccup at the start of the song. In other words, the song starts and it jumps/hiccups when it hits a spot between 2 - 5 secs. this happens to each and every song I play.

My setup:

Mac OS X 10.8.3
8GB RAM
CPU 3.2GHz
XBMC 12.2
Music on NAS
Streaming over WLAN
Music also Local HDD
Skin: AEON NOX
Music format AAC and MP3




While writing this thread I turned off the crossfade between songs which solved the problem. The option I am referring to is found in Music settings / Playback
Is this a known issue?

thanks

aussie