Over the last few months my GT has developed a really loud turbo whistle when giving it the beans (2.5k - 4k revs). It's had a new lower hose (this had split before and I replaced with a silicone one) and I've checked the top for splits.
Now I'd taken the car into my local Indy for a service a few weeks ago and told them about the turbo whistle. They confirmed it was the turbo rather than a pipe so sent it off for a refurb. Ive since had it the car back but the noise is still there.
There's no loss in performance or smoke as far as I can tell (other than a blue puff at start up). It seemed to start a few weeks after swapping the lower hose. Any ideas what it could be?