[924er]

Got my car back last week and I noticed that these turbos make a low pitched noticeable siren noise when the car is cold and gets quieter once warmed up. They boost fine tho, no rattle. I'm running e30 with FBO. I know many people have this siren noise when cold but is this an indication for failing turbos? I wanna make sure these snails aren't defective. The tech is blaming my downpipes for amplifying the sound. Maybe it's normal, what do you guys think?