Although I didn't have the sloshing sound I did have damp carpet recently in the drivers footwell and following the advice on here took off the wipers (I've got a 2/3 leg puller that was really useful as they are so tightly on the spindles) and the plastic trim at the base of the windscreen, on my 99 car there is a drain hole in the middle of the scuttle, a bit bigger than a £2 coin that was totally blocked with leaf debris, once I cleared that out and generally tidied up lots of other much in there it hasn't happened since. Only took me a few minutes to strip it all down although I did have to drill out the two screws on the far ends of the plastic trim as they had rusted and the heads disintegrated when I got near them.
Got to be worth a go.
Quick edit: If the centre drain hole is blocked then any water that has gathered could move across the entire width of the bulkhead so could account for a sloshing sound.
'99 156 2.5 V6 in silver with climate, electric roof and it's all working! Oh that noise....
'91 Golf Gti 8v in the garage, pampered toy.
Last edited by Andy1100; 24-10-10 at 09:07.
Reason: Forgot to add a bit of technical info