Rinse 500SE second stage question

Hi
When I turn on the gas to my DC7/500SE there is a "hiss-pop" as the valve in the second stage activates and I understand this is normal.
Does this mean that the downstream valve is not seated when it is unpressurized and can this second stage be rinsed or soaked unpressurized? (assuming as always that the purge is not pressed while doing this!)
Cheers
RR

The valve in the 500SE is a thick disc (~3mm), and we are told in the factory seminar that it is okay to soak the second unpressurized. That said, if I soak my regs unpressurized, I do them in two parts separately (though still connected by hoses: the first stage on a chair with the second hanging in the bucket, then drain/dry and then put the first with dust plug screwed down tight in the fresh water. But that's only when I don't have my pony, or a tub deep enough to have the second on the bottom, while I suspend the first just beneath the surface at the top of the tub.

If you look at the seat in the 500SE, it is a firm disc with cutouts at the edge to promote airflow. But it is not flat, and is slightly dished. So I assume the pop after the hiss is the thick disc snap-sealing against the depressed part of the seat where it just lay against the seat before. Should be okay to just dump both in a bucket of fresh water together, especially if you blow out the stages on a tank afterward.
But I try not to do it that way.

And even if you pressed the purge when unpressurized, you're only going to allow a little fresh/salty water into the small servo tube distal to the main valve. If the valve is lightly sealed as we are told, it won't flow further from there. It's different from pressing the purge in a typical 2nd, where pushing the button opens the actual LP valve.