Boxster engine whistle
 

My 2000 Boxster (non-S) 5-speed suddenly started making a constant frequency or constant pitch whistle. It has occurred twice, and in both instances the engine was fully warmed up, with the noise staring after about 20 miles of driving. In many instances of driving similar distances it does not occur. From the sound, and standing exterior to the car it is very likely to be coming from the engine compartment but from outside the vehicle it seems to be similar volume regardless of side.

It goes away with light throttle. As I said it is a constant pitch regardless of engine speed and occurs at idle.

Thoughts very much appreciated.

Long time member, I would suggest you look at the vacuum tubes. If that isn't it check your intake from the filter canister to throttle body. The tubes age and crack, a black 1/8" od. tube starts under Passenger side manifold (vacuum solenoid) to a splitter under the passenger side "T" coupler. onto the bottom of that coupler. then to the driver side manifold sensor, and then the front crossover tube butterfly valve. If you have a auto trans then the "T" is a 4 way with a tube going to your transmission.

https://photos.smugmug.com/photos/i-...-qWdhMFG-M.jpg

This is the intake from a donor "S" tiptronics motor. which was the base for my LN 3.6 build