What kind of a noise and what is loud?
A water pump will usually start with a rattle rattle sound or bad bearning sound. It will sometimes also have a small water leak coming from the under side. You can also remove the belt and see if the pully will move front to back (any movement is bad), or turn it with your hand and see if it feels rough.
My 1999 C5 coupe developed a rattle noise from the front of the engine. I took it to Mr. Goodwrench where I purchased it new and had the car serviced. I was told the a/c belt tensioner was bad - I authorized repairs. Then, the dealership called and said the noise was a bad power steering pump. I authorized repairs.
When I picked up and paid for the repairs, the same noise was present. I left the car for more diagnosis (technicians - not mechanics, don't forget it!). The noise was caused by a defective decoupler pulley on the alternator. The alternator was replaced (for very little cost since I screamed loudly regarding the two previous items that were replaced and were not defective). Noise gone.
My point in this long story - noise can fool almost anyone. The decoupler pulley noise sounded to me like a defective water pump bearing. Does your car have the revised alternator with decoupler pulley (which eliminates the A4 shift rumble)?