Not sure that I can help, but certainly willing to try.
You are positive this is coming from the fuel tank area?
Does the noise ever get louder?
Does it ever increase or decrease in repetition?
When you first turn the key to the on position, before you crank it, does the noise happen as the pump is being energized?
I know some GM have a pulse dampner, not sure on the beetle.
If you have the old one, can you hot wire it to observe any anomolies?
I need to read through my tech software to see if I can pry out something to work with.
I did find a tsb that my be unrelated, but want to share it regardless because I would gather low oil pressure may continue this condition:
Engine - Rattling Noise On Start Up (Normal Condition)
Camshaft Chain Tensioner(s) or Camshaft Adjuster(s), Rattle or Knocking Noise
The camshaft adjustment is hydraulically actuated and controlled by the engine oil pressure.
If the vehicle has been sitting, with the engine turned off for a period of time, the oil accumulation inside the camshaft adjusters partially bleeds off and the oil flows back into the oil sump.
To ensure an efficient camshaft adjustment after an engine cold start, the oil pressure inside the camshaft adjusters must be built up as quickly as possible.
During this time a slight rattle or knocking noise may be audible.
This noise is normal at engine start and will last until the oil pressure is fully reinstated.
I found another one regard the trunk lid. I want you to open the trunk lid and keep it propped while you see if the noise is still present.
Tuesday, October 20th, 2009 AT 6:04 AM