What is that noise in my dash? Waterfall - Bubbles - Rushing Water?

I just brought my 2003 VW Passat in for service as a few codes showed up indicating something was wrong with my coolant system… they replaced the t/stat and ECT. Now when I start up my car after it has been sitting for a while I hear a noise coming from behind the dash. It sounds like rushing or bubbling water being sloshed through a line. It gets worse during acceloration but goes away after a few minutes.

Can you tell me what that noise might be, and if it could be a result of the deal work that was done, do you think I could get them to fix it?

You have air in your cooling system; something the dealer should have worked out before turning the car over to you. I would take it back and have them properly bleed out the air.

Could it indicate a leak in the system that I will have to pay for? What would something like that cost?

Give it a day or two. Unless this is a real odd system (it may be), by the time you get it back to the dealer, it should work its way out. Assure that the recovery tank or expansion tank (whichever it has) is at the proper level.

I agree with Docnick. The car should not have been returned to you in this condition. They should have made sure all air was bled from the cooling system when they replaced the thermostat and refilled the system with coolant.

They should admit their error and fix it free.