Originally Posted by NSC5

The most common reason for this ticking is the cam driven high pressure fuel pump and it is present to a greater or lesser extent on all of the GDI engines using this type of pump to create the pressure necessary for direct injection into the combustion chamber. My first experience with this was my 2008 Cadillac CTS with a 3.6L DI and to combat the noise Cadillac used a lot of sound deadening to address the noise directly from the pump and also to reduce the noise along the common fuel rails which "sing" along with the pump. Corvettes have far less sound deadening around the engine (and in the passenger compartment) so the noise is far more audible. If my LT-4 equipped Z06 had been my first GDI engine it would have been more noticeable but after my first gen 3.6DI in the CTS and 2nd gen 3.6DI in my ATS the LT-4 tick sounds normal to me.

You can use a sound stethoscope to somewhat narrow the sound location and if it is the cam driven high pressure pump the noise will be louder near its location towards the top rear of the engine however sound propagates, especially through the common fuel rails, so it won't have only a single source point for the noise.

Also see this TSB for a related issue: http://www.corvetteactioncenter.com/...2017-1338.html

And on edit here is a nice post put up on the C7 forum by Theta that shows some good information on the layout of the HPCR (high pressure common rail) fuel system for those unfamiliar with its layout: https://www.corvetteforum.com/forums...e-for-lt1.html

And use proper caution around these systems since the fuel pressure in the rail is FAR higher than what people are used to with port injection systems and a little leak can effectively inject fuel into your skin. Although not as potentially dangerous as the HPCR used on diesel engines which develop rail pressures beyond 30,000 PSI the 2,000 and up PSI developed in these gas systems is nothing to be careless around.