Wastegate stuck when cold?
 

I have a 2001 Audi tt with a front mount intercooler air intake and exhaust when I havemy driven the car in about 4 or 5 hours and it's completely cool the turbo makes a tututututu noise compared to tge pshhhh noise it usually makes when I let off of the gas. When its cold it makes the noise even if I only pull a 10 on vacum to fix this i have been waiting for the car to warm up a bit and drive it like a baby until then and then ill let her rip and some times it will open it and other times it won't and I'll have to build higher boost the next pull for it to completely open but after that it goes right back to making the normal pssssshhhh sound I don't know if this is a common problem or something to do with the n75 valve please help!