Edit: I was typing this while Sky added his reply
For the 'running fast': while the game is running, alt-tab or press the 'Windows' key to get back to the desktop. Bring up the 'Task Manager', click the 'processes' tab, find gta_sa.exe & right click on it, click on 'set affinity' & uncheck cpu 1 so that cpu 0 is the only one checked. That should help your speed problem.
Edit: This may solve your sound problem also but if it doesn't see below.
For the sound, click the 'start' button & click on 'Run', type in 'dxdiag' (without the single quotes (') & click the 'sound' tab & set the 'Hardware Sound Acceleration Level' to 'Basic'.
Hope this helps.