The drivers door on my 2004 Ford Mondeo is leaking?

Hi i have recently purchased a 2004 Ford Mondeo TDCi. The car runs like a dream however it has one niggling fault which is whenever it is raining i can feel a very slight drip of rain when im inside the car i think it is coming from the drivers door and the same for the drivers footwell it is only slight and happens very seldom my question is how do i fix it? or shall i take it to the garage as it is under warranty. I shall look forward to your replies.

Many Thanks
Sean Sheridan