Dump Valve on non-turbo

Hi,

I have one of the 1.6 Primas. I have only just bought it. Whenever I change gear the car makes the DV tell-tale hiss sound. Its not a turbo so:

i) could it be something else (such as a fault)?
ii) can you fit DVs onto non turbo std engines?
iii) is there a benefit or was it some boy-racer type pandering to a 2fast 2furious fantasy?

Also, while I'm here, my fanbelt is loose, I dont want to take it to a garage, is it something I can do myself with relative ease?

Thanks