My engine makes a mystery tick that follows the rpm band up and down. I have smoked tested for exhaust leaks, replaced all of the followers and lash adjusters on the driver side and nothing changes. I think mine is just the tick that these get in cylinder 7/8 area and honestly, I have just gotten used to it. I figure I could rebuild the head and probably get rid of it but that seems to be a huge pain in the ass for something that probably isn't hurting anything.
If yours is louder on the drivers side towards the back of the engine (firewall area) I'd hazard a guess that you have the same thing I do. Everything that I have read suggests that these engines (and the Coyote afterward) can develop ticks in the valvetrain that don't really hurt anything and are more of an annoyance. Hopefully its something easy but if you can't pinpoint it and it sounds like what I described it might be the same thing.
2003 Mercury Marauder 300A
Former Owner: Joe Walsh
2015 Mustang GT PP
Guard Metallic Exterior
2018 F-150 King Ranch
2WD, 3.5 EcoBeast