The Subaru SVX World Network - Whistle/squeal from engine

Hi everyone,
I am new to this group and somewhat different as I have an SVX engine installed in a VW Westfalia Van. It is an awesome combo for travel. Anyway, I have a problem with my engine that is gradually getting worse. It started about 10K miles ago as a brief squeal when I shut the engine off. It never did it when cold and usually only after around town driving. Now it does it every time I shut it down, hot or cold, and also I can initiate the squeal/whistle by manipulating throttle while driving. I can also change the pitch of the noise by changing throttle position. If I back off or floor the throttle, it goes away immediately. I have listened in the engine bay with a hose while starting and stopping the engine and the noise appears to be coming from the Induction Control valve. Disconnecting the vaccum hose that goes from the control solenoid to the duty valve does not make a difference. Before I go ahead and replace the whole Induction Control Valve, I was looking for input to see if anyone else has had this problem. By the way, I have already eliminated belt squeal by removing the belts and then running it. It also does not appear to be a simple vaccum hose leak or manifold leak. However, when I first got this engine, it was burning huge amounts of oil until I rebuilt it, and I know the intake system was very dirty from oil and charcoal. I have already had to replace the Aux Air control valve and the Idle Air Control Valve as they were not working properly.
Feedback please.
Cheers
Steve