Hey guys and gals, just bought my 1st Audi a 2000 a6 180xxx miles. I have some records at 90,000 when the timing belt was done. How do you know when it's needed? Any warning signs to hear?

No warning signs. (unless you get really lucky and hear it screaming) The tensioner/belt will just fail. It's due now. 90,000 is about the upper limit for miles. If you wait for failure you will also get to rebuild one or both heads. Do the whole nine yards while in there. Water pump etc. Probably going to need some seals on the valve covers as well.

The water pump gets removed to replace the timing belt so might as well do this too. I now have 319,000 miles on my 2000 A6 2.7T

As previously said, there really aren't any warning signs that the belt needs to be changed. You could look for paint on the timing cover bolts to see if there is solid greenish paint on those timing bolts. The factory will put paint on those bolts to indicate that they either have or have not been touched for timing service. Even a visual inspection of the belt maybe ambiguous and leave you with more "what ifs" than concrete answers. You're better off having a piece of mind and changing it before disaster strikes.

I suppose it is a good rule of thumb when buying a used Audi to allocate about $500 (If you're a DIY'er) to do a timing belt upon purchase of the car unless you have records that indicate otherwise. From what I have seen on these forums, it seems that people tend to walk away from these cars around 90,000 to 130,000 miles when they get the news that they really need to change timing belts soon "or else".

Thanks to everyone's input. I was afraid to hear to just replace it.