That's shameful.
It sounds like the dealer just wanted you to go away, and stop bothering them since even they have no idea what the problem is.
Kind of hard to tell from your description what it could be.
Does this noise happen in cold weather, hot, or both.
Is the fan running for the climate control when you hear this noise.
How slow/fast is the thump?
Is this noise coming from behind the instrument cluster?
Let us know if there's anything else you notice about the noise, maybe we can narrow it down for ya
~Trail
__________________
93 Suburban 2500
203,000 miles on engine still running like a champ!
Tranny rebuilt at 197,000
My Daughter calls it the bus, and sits in the
third row seat praying for potholes and speedbumps!
Just Horsin' Around Equine Services
http://www.JHA-Trans.com