Today I replaced the lower intake manifold gaskets, then when it was back together I changed the oil and filter. Due to the manifold leaks, coolant got in my oil and brought it to a milky brown consistency. I drained the pan, dropped the pan, cleaned it out, cleaned the screen of the oil pump as best as I could without removing the pump. When I started it up, there was a popping sound that sounded like popcorn (about the same sound, and the same sporadic consistency) coming from the engine. Otherwise, the engine seemed to run fine, but I haven't driven it yet.

I've seen some posts about similar symptoms on this forum, but not exactly. They had the noise at higher RPMs, and mine is happening from the start. Any ideas? I'm afraid to drive it until I at least get a diagnosis on the issue. Is this likely a physical popping (two pieces hitting, etc.) or more of a backfire type sound (not physical, not actually causing physical damage). Thanks for any help!

Oh, and I can localize the sound to the upper intake manifold, or at least bank 2 of the engine. This is a 2003 3.0L V6.

 

Check that spark plug cables are on tight, reads like "spark arc" noise.

And double check firing order on Coil Pack and at spark plugs
Coil pack
3 4
2 6
1 5
Front

the 5 6 4 always gets me