When I picked mine up another chap was collecting the whisper version, so we both had a good look at it.

The barrel on the whisper is ported with multiple small holes drilled into the barrel for gas venting. The shroud is about the same but with an extra tube of aluminium inside to allow for better gas flow.

Unfortunately we couldn't shoot it at the time so I'm unable to say how much quieter it is. Caledonian do point out that it should be properly though - think of all the gasses condensing in the shroud. 10 seconds to strip for cleaning though.