hey hiko,

Just to reiterate Eurodude's point,

A sound coming from behind the dash/cdplayer/air vents can be anything from the engine bay area.

When i had a new exhaust system done, a squeak developed, and it sounded like its coming out of the dash. It was the flex pipe, which made the metal squeaky noise. I couldnt hear it from the engine bay, but heard it from under the car.

Might be wise to spend a bit of time just finding out roughly where its from (engine bay, front suspension, etc), might save you an arvo of opening the dash