Good day all. A problem has come up with one of my engines and I'm in the process of figuring out what's wrong and some input from everyone would be greatly appreciated. I have a 2006 Sea Ray Amberjack with 350 MPI Horizon motors, V drives (serial# range OW39000). There are approximately 525 hours on the engines. This is going not my 4th season with the boat. When I got it I was told that the risers and manifolds were done and it was evident that at least the risers were done (bolts turned and exposed unpainted surfaces). My fault for not obtaining written proof. With that said, I've developed at ticking sound on the port motor. The ticking remains constant with the rise and fall of RPM's. This was first noticed when using the boat this past weekend. Ran the boat at 3500 rpm's for about 30 mins. Temps were at 163 each engine. Did my first drift and when I restarted the motors I noticed the ticking. Continue fishing and then made the run back in. About the same amount of time returning to the slip. When backing in I noticed the ticking had quieted. Let the motor set for a while 10 mins or so and restarted. The ticking came back. The other thing I noticed was if I give the motor some throttle and drop it down to idle, the ticking will fade and then resume once at idle. I used a stethoscope and check the valve covers, heads, flywheel housing, pulleys, pumps etc. I never picked up on a "internal" click or tick. The sound seems external. There is rusts scale on the manifolds by cylinders 7 and 8. there is some rust on the underside of the others. I've given as much information regarding the issue. Before I'm committed on a diagnosis I would like to hear what anyones thoughts are. Might be something I'm missing. Thanking you in advance.