First of all, TU had the nice coin particle sounds from gmt once and i loved that, I'm pretty sure that that's a bug and hope that it will get fixed soon, but..
Another sound that gmt had was a very sweet and subtle high-pitched di-di-ding when you clicked the purchase button, i don't know if this is a copyrighted sound from another videogame but i really really liked it. If people like this suggestion and its not hard to add:
Can we maybe have that sound or a remake (in case of copyright etc.) in TU too?