Strange problem, basically no matter what source I use, radio, ipod or CD, when Nav route is running the audio glitches occasionally, like a stuttering. If I clear the route, there is no glitching at all.

Any ideas?

Voice instructions from the in-route map. Use a modded Data.zip, one that gives you the option to mute the instructions.

Any idea how to do this then? I thought it could be the nav voice

Most any modded Data in the hacking forum has this option. Ildietrying, GTIMatt, just to name two. Read the threads to find out how to put the unit into testmode and copy the zip over. That being said, if you don't feel comfortable doign this, dont. Read and read more. But I will also say, the only to get comfortable hacking the unit is to do it.