Fiestas are known to collect water inside the doors from raining or when washing your car and it builds up inside. This happens when the drain holes at the bottom of the door block due to dirt etc. Look around the bottom edge of the door from the inside. There is usually two or more rectangular holes about the width of a penny. Use something thin and long and poke through the holes and watch it pour out! Check this reguarly otherwise the inside of the doors will be prone to rusting.
Hope this helps!
Thanks for this... sounds nice and inexpensive! :-) You're probably right as it has been raining here a lot lately and it's only since then that it started doing it. I'll try that tonight and hopefully it'll solve it. Will let you know if not. Thanks again