We know, lol.
Yes, a small leak can go away with it warming up, the metal expands applying more pressure on the seal.
Yes, a lifter tic could go away as well when it pumps up.
I will say this, if you are running a Comp cam, some of them have a very fast ramp and sometimes people experience what seems to be lifter tick when actually it's the valves snapping closed. Mine does it a little, drove me nuts for a while until I researched it.
Here's what I would suggest, grab a piece of hose about 3 foot long or so, let the engine go cold. Start it up and use the hose as a stethoscope to listen around the header flanges, one end on your ear and move the other end around the flange, if it's leaking you will probably find it. I'm betting it might be since you said it quieted down after you tightened the bolts.