964 Squeak-squeak-squeak

[Newsboy]

I have had the 1990 Carrera 4 with 62K for a month. It came with a Squeak-Squeak-Squeak(high pitched) sound which appears to be coming from the passenger side rear.(louder from passenger seat). This sound is pretty constant above 1500 RPM, although you must listen for it above the sound of the engine. If I stay below 1500 RPM, the sound is not there. If I put the car in neutral, or step on the clutch, it stops in about 1 second. This would seem to rule out wheel bearing, CV joints etc... I can't get the car to make the sound by standing with the engine lid open and applying throttle(so not a belt) So could this be drive tube/drivetrain related? A friend who is a foreign car mechanic(although not familiar with Porches) thought it sounded like a vacuum leak. Any help in pinning this down would be appreciated.
Thanks