My Sovereignty upgridded G-line 75mm with natural splash guard makes a vacuum sound when being pulled. Because of the way the g-line and perhaps the natural splash guard work together, it makes a very powerful pull and it works great with a vaporizer because the pull can be very subtle or very forced. loudest
My Sovereignty downgridded Stemline doesn't make much noise, it's more of a flowy percolation and sounds more slushy and constant, not as loud and definitely not like a vacuum like the other piece. Feels more free-flowing, better for large flower rips (combustion)
My 60mm Stereo Matrix by Mobius makes a very faint, burpy-bubbly sound. I like the sounds that it makes. It works great for flower rips or dabs or vaping or kief, very versatile little piece, I love her, though I do not use her much lately, once I get shatter I'll try that in the evo, connecting a silicon hose at the top of the vapexnail and into the 18mm male opening of the Mobius. most quiet