Evenin all, Since I’ve owned this car it’s had a lot of noise coming from the rear of the cabin with the roof up. I can almost hear everyone reading this muttering that the valves are stuck open in the drains. They are/were. I’ve prodded and poked, stuck the trombone cleaner through them in the correct direction multiple times to no avail. So I followed a little piece of advice I found on another website. Aquarium foam. This stuff is designed to allow water through but not anything else [like fish presumably]. I bought a 2ft square piece and cut a couple of small chunks off. Inserted into the bottom of the drains and the noise is gone. The water still flows well through the foam and when i need to clean the tubes they pop in and out easily.
Hopefully that’s of some use to somebody!