I have an some aftermarket equipment in there, namely a Pioneer stereo and its accessories. I have had the dash apart a bunch of times looking for rattles, but to no avail. It sounds like it is coming from behind the radio or center air vents. Any ideas or previous experiences??

Until the noise stops, or changes. Then have them look in there and see what they were touching.

it is coming from behind the instrument claster.
Steering column ?