I've been hearing what I thought was noisy injectors, coming from my engine bay for a while now. I was finally determined to figure out why my Cruze was so much louder than the rest. Found it to be the Evap purge solenoid, mounted to the intake maniold. Once the car is warmed up, and the valve is "purging", it repetitively clicks, many times a second, almost synchronous with the firing pulses of the engine. Unplug the wire connector, and it stops. Anybody else ever have this issue? A new AC Delco part is only $20. May replace it and see what happens.