Ok I realise it's a bit of a longshot, but there is a piece (which I have been told is buy Mozart) that is very famous, I knew it immdiately, and I believe to be played on piano.
I can only describe to you what the main theme goes like:
If you imagine it starts on a C, It would go: CBABC, DCBCD, EDCDEDCDE,
It's fast and I would imagine the first 4 notes of each "part" (eg CBAB) to be semiquavers or even shorter.
It's very twiddly, and damn it I can sing and hum it but can not for the life of me describe it!!
Hope you can help, I feel ever so silly!
Best of luck searchers!