I picked up a brand new Esseesse 2 weeks ago (Snows Hampshire) but due to this and that it's only done 50 miles so far, and has been garaged the rest of the time.
Initial runs no issues; Drove it back from the dealer, and then a round trip to town with no issues, and then on the 3rd trip out after pulling out of our parking area, round a little turn and then pulling out onto a main road onto a straight and accelerating we all heard what sounded like water sloshing/gurgling/trickling from behind the dash (more left side, say behind the glovebox) and it was loud enough my dashcam picked it up.
After a slosh or two it stopped and it didn't happen again until a few miles into the return journey.  Next journey out on the first straight bit and accelerating it did it again but was then fine and didn't happen on the way back.

It was inside the showroom and has been garaged the entire time I've had it, and so the only time it has got wet recently was when they washed it just before handing it over.  I have heard of water gathering in the scuttle
panel/tray but it doesn't do it on cornering and I've had as good a look as I can without taking it to bits and it looks dry in there, so sign of any water.

I initially asked about it on FB and the consensus was either blocked scuttle, air in the coolant system or as the
 heater matrix is around that area it could be normal operation as it adjusts and the water pump is circulating the coolant.

It's going back to the dealer to get a seat badge fixed (found a tiny snapped piece on inspection) next week, and I've asked them to take a look at this issue at the same time so if I can give them some headers that would be helpful.