Ok, I had my 454 mag EFI (385 hp) engine rebuilt 2 years ago. Since then Ive put 50 hours on it. The boat runs awesome (tons of power and it sounds perfect) but this morning I noticed a loud ticking noise coming from the back of the motor (at idle). I cant seem to isolate it to either side. It just seems too loud to be flappers. I havent even run the boat hard this week--Im in AZ at the Desert Storm (nothing over 4000 rpm) but it has been sitting all winter (this is the first use of the year). Im guessing a stuck lifter. What is the best way to free it? Additive?

Exhaust flappers can sound like a rod knock and nearly as loud. Put your hand on the rubber exhaust hose and you can feel them.
If the noise goes away when you throttle up to about 1200-1500rpms, then its probably internal exhaust flappers.

Ok, well I revved the engine up to 1500 rpm in neutral and can still hear the ticking noise. Still kind of scratching my head here....Lots of power and the engine sounds perfect from 1500 to 4000 rpm (i havent gone past 4000). should I worry about this? Possibilities are valve, rocker or spring right? How would I diagnose?

I guess it could be a loose rocker arm. You would have to pull the valve cover on the side that is ticking and check the rockers, could make a bit of a mess though.

Take a piece of water hose 4' or so and hold it to your ear then swipe the valve covers with the other end till you can hear the ticking and locate exactly where it is. Works just like a Dr. Stethoscope

You need to isolate where the sound is coming from. Consistent ticking is usually in the valve train. It could also be a leaking exhaust manifold gasket.

I had the same thing happen last summer on a 27 baja 454 mag 385 hp. I pulled the valve covers and checked for loose rocker arms etc, all looked fine. I finally said screw it and just went boating as usual.

I am going through the same thing right now. My problem was my exhaust manifold leaking. They are replacing them now.

check you exhaust manifolds for leaks. if your motor has the same power then its probably not a lifter. Exhaust leaks definately make a ticking sound.

Just checked and this is what I saw on the starboard exhaust manifold. Does this look bad enough to cause the tapping sound Im hearing? The other side of the manifold appears to have more leaking and some signs of rust. I tried to tighten the bolts but couldnt tighten them at all.