Troubleshooting tip: intermittent hiss noise from rear

[Turbolader]

After pulling my hair out on this, I wanted to let anyone else know about it before pulling all their hair out.

If you are trying to track down a short length (0.5 sec) hiss (Think "Psssst") from the back of the car when:
1. you start the car
2. around the shift points

The source might be the pneumatics controlled by the muffler flapper solenoid. The controls are in drivers rear section of the car.

This is not to be confused with the surge/blow off valve. (Much higher frequency)

In my case I happened to hear it because I had the drivers rear panel off (I am installing my amp behind the large metal panel where the stock logic7 amp normally lives). There is a lot of sound deadening material covering that area, and I think that mutes it so you normally never hear it when driving around.

If you think this is the culprit, you can test it by:
1. Putting everything back together (Not best if you still need amp out to set levels)
2. Pull wiring harness to valve (This does set a 'hidden' fault code...but this is how I tested it)
3. I suppose that you could pull the source vacuum line and insert a golf tee (or use a vacuum clamp without pulling the source line)

I don't think doing the gold-tee mod will fix the sound because the sound comes from the solenoid in the trunk area and not the valve in the muffler.

Anyways, hope it helps someone if this comes up during a search