[tolum]

Here is what I did for my 2003 Boxster 2.7 (maybe P/N are not the same that you need):

There are two (2) solenoide valves press fit in a valve housing behind the gas filler section. Accessing that valves housing is done by 1- Removing passenger front wheel and plastic wheel well. Valves housing will be at top right of the wheel well just behind the front headlight. The housing is bolted up there, so unbolt it.

The best way to access and remove the valves from the housing is done by going by the passenger side front headlight that you have to remove first. Use a flash light and you will see the valve housing that you just unbolt. Inplug power from the valves (both terminals are different, you can't mix them. There is a plastic sleeve that cover the valves. Use a Torx screw driver to remove it. Pry gently the valve metalllic ring and voilà!

First of all I did order Shut Off Valve P/N 996.605.201.01 ($72.00) from Sunset. Did replace it but it wasn't the good one, noise was still there. Did order the second valve P/N 996.605.213.01 ($41.00) and noise gone!

See att. pictures of the valve itself and the drawing showing both valves position.