with the carpets out for a few days weve dried it up and although I have fixed a small issue of SOME water coming in from a rust pinhole from puddles and splashback it wasn't the major cause. The carpets masked the problem being so wet you couldn't see where it was coming from, same with the sound sponge.
It had rained hard overnight, I checked the car myself this time in the morning (instead of third party Chinese whispers) ONE groove nearest the door had water, rest of the car bone dry. Felt around the doorframe, no water I could feel.
The 'sucking' and 'sloshing' noise got me wondering and because there are two rubber seals on the inside of the sill/chassis I took them out, one was bone dry the other was all wet and slimy inside the sill - this means water is regularly in this area and sitting there.. same slime as the scuttle issue I had in the 156, where slime builds up from static water.
So, my theory at the minute is when its really raining hard the water is building up so much its overflowing into the footwell. The sucking and sloshing is the water inside the sill (and pressure through the rubber bung)
Next thing to look at - where does it drain off to in the sill (for blockage) and also what feeds into this drainoff area (ie. roof?)
This could be similar to why Artermis had a drain one way, not the other
I only had 30 seconds to look, so more investigation to come....