I just replaced the exhaust manifold gaskets on my '89 740 Turbo with 115,000 miles on it. The car seems to have quite a bit more power - no surprise there, as the exhaust leak was probably reducing the efficiency of the turbo. But, the strange thing is that I now have a whistle at high boost/high engine speed, say 4,000 rpm with 3/4 to full throttle. This is NOT the siren noise I've heard on turbos that are on their way out. It sounds like a very high pitched version of how I remember a burned valve sounding on an old VW, years ago. I was as clean as I could be with the oil supply line to the turbo, but of course, my concern is that I somehow got some dirt into the turbo bearing anyway. Or, maybe the now higher boost is accentuating a leak somewhere in the intake.

I have the Mitsubishi turbo.

Any suggestions? Thank you.