I have a 1982 245T. The turbo has been replaced with a water-cooled unit. The mileage on the turbo is approx. 30,000. Two days ago the car started exhibiting a rasping/hissing noise at WOT. The boost gauge readings (or behavior I should say, as it's stock and, as such, devoid of numbers) haven't changed, neither has the seat of the pants acceleration. In fact, nothing about the vehicle's performance seems to be worse.

It tapers off as I let off the accerator and boost drops. The noise hasn't always been there and it appears to have gotten slightly louder (although I could just be getting more sensitive to it).

It sounds a little too "rough" to be a vacuum leak but not rough enough to be a mechanical interference. I am at a loss as I can't think of anything else except vacuum. If it WERE vacuum related, wouldn't I have other maladies i.e. rec-def-floor switch intermittency, idle flucuations, turbo anomalies?

Any and all thoughts would be appreciated.