Noise from behind the dash

I have a '99 Malibu that is making a slurping noise from behind the dash board on the driver side when it rains. It only does it while I'm driving. When I come to a stop the noise quits. Does anyone have an ideal what could be causing this...?

Don't worry. It's very annoying but there are two reasons it can happen and both are fixable. First, There is an area against the firewall which collects excess water - rain, washing etc. You may need a service dept. to access it. There are drain holes in this catch basin(sorry for non-technical terms). If these holes get clogged with debris, the water buils up and starts splashing around. That's why it happens when it rains.

The second possibility and the one that plagued our Malibu is a bad seal in the gasket that goes around the edge of the winshield. Water can leak into the catch basin and slosh around. Our mechanice had to pull out the windshield, put on a new gasket and reinstall. We have not had the problem since that time and it no longer sounds like waves inside the engine compartment when it rains!