Run everything at stock and disable the on-board sound at the BIOS level. Sure it most likely won't do anything but it'll eliminate potentials.
Run Steam.exe with administrative privileges, possibly disable UAC for the time being.
Disable the Steam overlay and cloud support through the settings menu on Steam, check any of the other settings there too which may be worth playing with.
Minecraft isn't exactly the most taxing of games so it might be worth finding a demo of something to download, not through Steam though. This is just to verify absolutely if the problem lies with Steam or something else.