Check everything is sealed properly, air box etc.
Alternator noises tend to be more like a rumble, or a squeal from the belt. Are you experiencing any other problems, e.g. warning lights on, slow starts, dimming lights?
You may also want to get it scanned on VCDS for any faults logged.
If you live anywhere near Lincoln I can recommend LVWS on the A47 for an honest assessment and they won't rip you off either.