As your the engine is running crack the injector lines one at a time and see if the sound goes away. I have done this before on a 606 its cake.

If you crack a line and it goes away you have found the bad cylinder or more probably a bad injector. Swap that injector with another one and see if the sound follows that injector.

btw you need a special socket to pull the injectors on a 606. They are not expensive about $30 last I checked.

__________________
2016 Corvette Stingray 2LT
1969 280SE
2023 Ram 1500
2007 Tiara 3200