humming noise

[dolinsky@esslink.com]

I have a 1993 quattro v8...great car...but, yesterday it developed a humming 
noise at speeds above 30mph. It almost sounds like the engine, but it is 
something else as the noise does not change when i put it in neutral and drop 
the rpms..it is not a very high pitched hum and it is not loud, but its there 
and i am sure it is the beginning of a problem..does anyone have any thoughts 
on what it may be..I will be taking it in to audi to check out but would love 
to give them some direction as they tend not to do anything until a major 
problem develops...