What should an engine sound like?

I just broke in the cam in my 360, I changed the oil after the break and today I had it running to check oil pressure, temp little things. I was listening to the actual engine and could hear a slight noise, definitely wasn't a knocking noise, and it was coming from the top of the motor. It just sounded like valve train noise (I think?), kinda like a really quiet sewing machine or something. Valves are all adjusted good. It's really quiet, I can only hear it if I stick my ear close to the valve covers.

It's a comp extreme energy flat tappet cam, I've read that they can be kinda noisy, could that be what I'm hearing? I also haven't timed the engine completely, I just had it going for a few minutes, I'm planning on timing it and getting it ready to go for a ride this weekend.

Should I be concerned about this? Or is it to be expected? Slightly worried...