[mightymoose_22]

You can still do a compression check, just for the sake of doing it. Doesn't take long.

You might also just disconnect the cat from the exhaust manifold... or just disconnect the entire manifold, and see if the sound goes away. That would cost you a gasket.

You can also try and listen with a stethoscope and see if you can isolate it. Something that sounds like the starter might just be resonating through the intake manifold.

If after doing all this, and removing the oil pan... you are pretty much stuck in a position where you need to go ahead and pull that head off. Every time you run the engine you are probably causing more damage though.