I have a few lifters making noise until well warmed up

Your description sounds like lifter bleed down to me. My though on it not doing it every day is it's not all the lifters bleeding down and some days the engine stops with a good lifter(s) compressed and it doesn't bleed down so you have no noise that day.

BTW: does that synthetic oil your using have plenty of ZDDP in it? If not it'll trash your cam and lifters. Unless it's Royal Purple or one of the other racing synthetics you need to switch to Valvoline VR1 or an equivalent before it's too late, if it isn't already too late.