I can say that mine sounds like an intermittent NOS purge valve noise coming directly from the middle of the car underneath.

 

"when I had the back seat out, I could hear the fuel pump clearly....it seemed like a high-pitched humming more than a 'hissing' sound......... "

Well if the fuel pump hums and doesn't hiss..then we are all dealing w/ something else! I only hear it when the car is at normal operating temps and is either in park or neutral(5AT).

 

I've had the same problem since I bought the car and a friend of mine has the same problem too, I think its normal but not sure what making the noise

 

Alright, I'm told that this is completely normal. I actually went to the dealership like a month ago and told them that there was a hissing sound coming from the bottom of the car and they told me that it was the fuel pump and that there should be nothing to worry about.



2004.5 G35c, Laser Red, A/T, Black Interior, Premium, Aero, & Wheel Package.