Strange Sound at High RPM - 2007 Black Scorpion

[DZP1]

It's not a Moomba - I know! But these engines are used throughout all models and I am stumped. I bought a 2007 Centurion SV240 last spring with 225 hours on it - it has the 330HP Mercruiser Black Scorpion. Ran fine last year. Winterized (by marina) and in spring I replaced the cap, rotor, wires, plugs, fuel/water, fuel filter and oil+filter. Now this year there is this weird banging/flapping sound that occurs intermittently over 3500 RPM. The boat does have the Sideswipe (sorta like captain's call) exhaust. Pretty difficult to pinpoint where the sound is coming from so I'm looking for some ideas on where to focus my efforts.

Anyhow, does anyone have any ideas or have you had this problem in the past? Video link below. It happens right at the beginning and then again at about 3-4 seconds and then throughout seemingly randomly. I tend to think it has something to do with the corsa sideswipe system, but cannot pinpoint it yet.

Thank you for your help!

https://www.youtube.com/watch?v=NVb7-_SEn20

[SONIC]

First thought is double check your plug wires for firing order.
If you mixed 2 of them up it could cause that and a loss of power.

[DZP1]

I will do that. Thanks!

[HFarr]

Sounds like a misfire to me. Could be timing advance not quite right too.

Sent from my moto z4 using Tapatalk

[DZP1]

Thank you - I'll figure out if I can adjust the timing - though I don't think I can on this engine.