[MHGinTN]

Having fired an Uzi with suppressor, in 9mm, I can tell you that the loudest sound was the slamming of the bolt.

[Billthedrill]

Wouldn't doubt it - the HK was in 9mm as well. Seems to be a good caliber for that. I shot one - a sort of antique model - affixed to a 1911 that wasn't much better than a Coke can...

Some of the best are in .22 LR, by reputation, but I've never had the opportunity to try them out.