The only sound level testing I have done has been on the Propex itself. Measured with a dBa meter at approximately 12", on the bench, the HS2000 shows 63-65 dBa. The HS2211 is a tad quieter at 55-58 dBa.
There is the propex marine hull fitting that will terminate both pipes in a sidewall, we've sold a few of those to truck camper manufacturers, although I like the single port models available from other sources and may soon stock a few of those. One batch of 18 we sold to a truck camper builder in the US for distribution to Iceland just ran the pipes out on a sidewall, less than elegant IMO.
How about the noise level from the HS2800? I'm trying to decide on either the HS2000 or HS2800 for my camper.