Hmm! How shall I describe it...dry, slightly gritty ssshhhh sound,I don't know if I can define it any better than that. It is, to my ears anyway,clear as a bell when you get it just right. No. not slippery! This is most clear when stropping on a leather/wooden paddle, not so much on the WEPS strops.
I am talking here about stropping with green,gold,red or black compound. Diamond paste or spray does not have a distinctive sound to my half-deaf ears.
Clear as mud eh!

Leo

I would describe it like a hiss of a snake. When the strops are wet with diamond paste, you dont get much stropping because the strops are kind of "ice skating" on the blade. Let the paste soak in for a good while, work it in real good, and for the first few knives, after a few strokes, clean the paste that leaks off the strop off of the blade, until the strops leave no more paste on the blade. NOW you will be getting results, as the diamond paste impregnated in the leather is sliding on the metal, abrading it, and not the leather sliding on a protective layer of paste. You should see no paste on the bevel.

Ed is right on, as usual!