Originally Posted by Vargasturbotech
Turbos should not I repeat not make that noise, a whistle is 100% normal and with less restrictive exhaust you will hear it more. With a siren or as its called turbo howl your turbos are well on there way to going out. The noise is caused by excessive play in the center section, either in the journal bearings radial play or in the thrust axial play, usually its a combo of both. This allows defelction under boost as the exhaust imparts force on the turbine wheel, the excessive play allows the compressor wheel to actually slightly contact the compressor housing causing metal to metal contact and this noise. Once this occurs it actually starts to machine away the blades of the compressor wheel a little at a time and it will eventually throw itself out of balance, take out the piston rings and everything else with it, and you will start smoking badly. Another thing I have seen with stock turbos is, the turbine side piston ring allowed excessive oil to escape past, which gets under the heat shield and from the extreme heat turns into carbon and as this builds up under the heat shield it pushes the back of the heat shield into the back of the turbine wheel, this can also cause this noise with the same results. Bottom line, turbos are on the way out, next thing in the time line is smoke. Hope this helps.
Thanks for the info Tony. It looks like alot of us are in for a suprise