You're right, my ST is super smooth also. Different sound than the Aria, and heftier (I have the AA battery grip on mine.)
I'll post it if someone can suggest a place that hosts audio;
I have to second this. As well I would add the conTax RX/ST. They are motor drive cameras with silky action. Hard to beat. The RX/ST may take the prize for least vibration simply out of having more weight than the Aria.
My Aria is not even close to the Nikon F80. Nonetheless, I personally prefer the Aria and never use the F80, but that was not the question here.
I understand the main question is smoothness and that is what I'm speaking of. But since someone asked, I did make a recording of a few shutter sounds for some inquiry before. I'll post it if someone can suggest a place that hosts audio; I lost the host I had previously. IIRC cameras were Nikon F3 w/motor, Leica M2, Nikon F80, and Rolleiflex. I thought it was a fun clip.