What's That Sound?

I rebuilt the top end of my 360 with new heads, intake, cam, hydraulic lifters, and carb. I had an oil pressure prob at startup and shut it down until I could get a rod and prime it. Then went through the break-in without issue. I went to the muffler shop today to get the exhaust all patched up and on the way home right outside my neighborhood, I heard this tapping sound. Oil pressure is and has been around 60 psi.

Sadly, I think I know what it is...but what's your guess?