Looks like most just completed the survey and never came back to this post.
I assume tons are just like me. They heard this sound mainly after they tuned their car. It scared them at first. It was mainly noticeable with cold temps and cold engine temps. It's not changed significantly since first noticed and their car still runs great.
In my case I do plan to go to Vargas or RobBecks when I get the money in a few years but I am not really worried that my overworked turbos are gotten suddenly go out. My 135 has been FBO and tuned and has had the siren noise when cold for 3 yrs or so. No performance loss and I actually barely even notice the siren anymore although I doubt it has gotten better but for sure it hasn't gotten worse.
Funny enough I don't really know why I plan to upgrade my turbos, even with an LSD, anything over 400+whp/tq just spins the heck out of the tires anyways!
Injen, RR OCC, MadDad Whisper, donut spare, 19x8.5et43fr 19x9.5et45r Volk LE37's, rear fenders rolled/pulled, Nitto 555 225/35fr PSS 255/30r, KW V1's, AR coated catless dps, Cross strutbar, CF grills and license plate holder, rearseat removal, iCarbon diffuser and front lip, ETS black anodized FMIC, M3 control arms, Quaife, ER chargepipe, ForgeDV's, Topspeed Custom Tune, V3sims, Braille, Andrey_GTA rear hub mod.