Did a complete water pump/ timing belt kit
 

I have a 2004 A6 3.0 Quattro wagon, recently had a noise coming from water pump so I parked the car immediately so as not to damage the engine. I bought the new water pump and timing belt kit, got the tools to hold cams and everything in place and proceeded to take apart. I lined everything up-timing is dead on and adjuster pulley near water pump has two key holes facing towards water pump ( I was told that it mattered). I put all new fluids recommended by Audi, I can start the car with no engine noises, no dash lights or codes, but have a hum noise that is coming from the mid area of the engine front. I took the car back apart to where I could tie tranny lines together, etc. and the car makes no noise after quick start and run? I put everything back on again and the noise is there???
Are there known problems with the main lower serpentine pulley? What could cause this? So very frustrated and have been working on this car for a month-out of money and out of patience-PLEASE give me some ideas, maybe there is one I haven't tried yet. The engine has full compression, I just don't dare to drive it and I have limited foreign auto repair people in my area-everyone has Subarus!

is this the same noise as before? or a new noise. Listen with a stethoscope?