Noise from OSB on floor decks is usually from their ends or sides moving - are the boards tongued & grooved (T & G) ?
It is always advised that boards are glued to each other and at their ends, and that their ends are alway, always, supported.
If you google, you should find a paper on this from the Wood Panel Industry Federation - WPIF - on how to lay OSB decks. PM me your email address and I'll send you an extract if you don't find it.......
I would not put thinset mortar or screed on OSB - it will crack. What you can do, and I just did, last week, is to put Hardibacker board over the deck, and you then tile that. Hardibacker is a cement based board that won't shrink, move or absorb water, and is specifically for tiling -either walls or floors, and comes in 6mm and 12mm thickness'.
I've used it in several places, and it's great.