2002 Z71 Surburban buzz noise in dash

My Z71 has always had a buzz noise in the dash on the passanger's side. It sounds simular to a small motor running/buzz. It only last for 2 or 3 seconds and usually does it from an excelleration after slowing down. I have had it at the dealership approx 9 times and they can't find it, they do hear it but hard to locate. Has anyone got any ideas? I am about to run out of warranty and would like to have it fixed.