What is wrong, if anything?

[ProjectM96]

Sometimes when I am driving my 986 2.7, there is a sudden loud vibration coming from behind me. I thought that the wind deflector was just shaking more than usual, but when I held the wind deflector down in place, the noise was still there, so that was not it.

When I step on the clutch or put it in neutral, it stops. This rarely happens. Does anyone know what it could be?

FYI: I have the check engine light on for the secondary air system like most Boxsters get sometime in their life. I plan to replace the cut-off valve when I make the money. But I doubt that has anything to do with the vibration. No other CIL codes or warning lights. Wheels are on tight. Tires are in great shape.

[kabel]

engine mount?

[clickman]

Is the vibration around 3000 rpm? If so, join the club. As was suggested, you could try replacing the motor mount (as I intend to do this spring). Others say its the clutch. Others say its the exhaust. A forum search will get you lots of hits.

[ProjectM96]

Engine mount is exactly what i was thinking. It was around 3000rpm.
Exhaust feels tight to me. I don't see how the clutch can make that kind of noise. It's got to be the engine mount.