I recently test drove a 1999 V70 T5, and while the engine was idling, I went out to take a listen with the hood up. What I heard was a pretty loud clicking (although I couldn't hear it with the hood closed). However, the clicking was NOT coming from the valve cover like you might think, it was clearly coming from the aluminum fuel rail that is just in front of valve cover and just on top of the intake manifold. I was able to confirm this by putting my fingers on the rail itself, and very clearly feeling a knock resonating through the rail. It was almost as if someone were tapping on the rail with a small hammer in time with the engine. When I put my hand on the intake manifold and the valve cover, I felt no such clicking.

Is this click normal for a turbo V70? I have no idea what, inside the fuel rail, could cause this pronounced click, but it makes me worried. Any ideas?