There is enough examples on the web of people who have had turbos with no noise failing and turbos making siren noise for years that the noise is not a reliable indicator of imminent turbo death. As already suggested you need to use vcds to check for codes related to boost. Who is your warranty with? Audi or a third party. The small print on third party means it's highly unlikely you will get a new one from them. I see you have a remap, unless Audi mapped it I would keep quiet about that and remove it from your signature- small world these days!
I swapped a turbo for the same reason. On inspection there was no bent shafts no damaged blades, turbine shaft was on the Mark for Garretts diameter and bearings looked like new. I fitted new bearings and seals to it and had it balanced it's on eBay now- shameless plug sorry!
Check your oil level as these turbos need oil not just for lube and cooling but also for taking the slack out between the bearing outer and the bearing housing. The turbo I fitted was another one I fitted bearings and seals and had balanced it whistles a bit in a nice way.
