I have an 18 month old Renault Grand Scenic, still under warranty. Following heavy rainfall, there was strange whistling noise from the air vents. Water then began pouring into both driver and passenger footwells.

Renault tell me that it is due to debris falling through the grills and clogging the drainage. The overflow apparently leading directly into the interior of the car. Surely this is a manufacturing fault?

They say it now needs to be dismantled to be cleaned - NOT covered by guarantee - even though I had a service done six months ago. So not only do I have to pay for a manufacturing issue, but also for any potential water damage done to the vehicle. What should I do?