Intermittent whistling passenger side 2000 boxster
 

I have 2000 boxster. I hear an intermittent whistling sound at low speeds more often when turning right. Sound does not vary with speed. Sound lasts couple of seconds. Sound goes away when I accelerate or let off gas. Sound coming from passenger side of vehicle. Any thoughts?

There's a vent in the gas filler area forward of the hinge (not the one just below the cap, which is a drain). Not sure of the parts involved in each model, but it relates to the filler mechanism. For me, just putting a piece of gaffer's tape over the hole solved the issue.

A faulty AOS can also make a whistling sound....
Try removing the oil filler cap while the engine is idling - if the cap is difficult to remove (a vacuum being pulled), it's a good indication you need a new AOS.

I have a bone stock 2003 Boxster S 3.2L 85,000 miles with a whistling / kazoo / howling / blowing into a bottle sound coming from the fuel filler vent behind the fuel door. It has made this sound for years. Finally it got so bad that it would make the noise at an idle. I replaced the Carbon Cont Value 996 605 213 01. It has been a week since I replaced the value and the whistling has not returned. In addition it fixed what I had thought was a minor vacuum leak, manifesting as a low rpm stumble between idle and 2000 rpm vastly improving the drivability of the car at low rpms (think crowded 5 mph parking garage).

To replace, remove the passenger side headlight. Look into the fender with a flashlight and you will see two values that appear identical, you want to replace the second value but will need to remove the first to get access to the second. Remove the electrical connection from the first value. On my car I used a T-25 torx to remove the screw between the two valves. The torx was in so tight I needed to use a ¼ ratchet with a 3 inch extension, any longer and it will not fit in the fender, any shorter and it will not clear the first valve. Once the screw is removed, slide up the collar holding the values down. Using a flat screw driver (I used a panel puller) gently pry up the first value and set it aside. Mine came out easily. Now pry the second value out, disconnect the electrical. Keep everything clean, I had a few sand particles around the value seats. You do not what sand on the O-ring seals or in the evap system. Reverse to reinstall. It took me about an hour most of which was getting my tools ready and protecting the painted services and then putting everything back. The actual procedure takes minutes if you do not drop the screw in the fender!