Engine wet exhaust clacking sound

[NotreVoyage]

Any suggestion on the cause of "clacking" from my exhaust, I think it is from the exhaust. See video link below.

The video sound is not perfect the sound is a definite clack. Sounds like a leak in the exhaust. The normal exhaust outlet sounds normal and plenty of water flowing and with the lids closed it is not particularly noticeable. The engine was recently lifted for new mounts and oil seals. Engine is a Westerbeke 3B30 and this makes it sound like an old tractor engine, which it is (Mitsubishi L3E).

I have:
Sprayed everywhere with soap water - no obvious leaks.
Replaced the top hose (engine to box)
Removed the water box and pressure tested it. No leaks. Not a high pressure test just a standard bike pump with rubber seal and hand blocking the outlet. The box is simple just an empty box with an inlet pipe and an outlet pipe at the top that extends 75% towards the bottom. Hard to imagine anything to fail.
Rubbed the box to exhaust outlet hose with soapy water no obvious leak and no change in sound (like going over a weak area).
Poking around covering things etc produces no change in sound.
In gear out of gear makes no difference.

Any suggestions welcome:

Video;
https://youtu.be/Eamx8ZqfI0w

Thanks all

[Cheechako]

That sounds like normal diesel valve noise to me. I think... !
Somebody doesnt have a one way bronze flapper in the exhaust hose do they? nah, that would stay open not flap...

[jkishel]

Well, I don't hear anything unusual, but that could be the recording, my speaker, etc. However, this is a wet exhaust system and the pressure in the hoses and muffler is slightly above atmospheric. So if there is an exhaust leak, you will experience cooling water (sea water) leaking into the boat. No need to apply soapy water to the hoses and fittings to detect a wet exhaust leak. I suppose with new engine mounts something attached to the boat like a locker cover, strainer, companionway board, or some piece of cargo could be vibrating that didn't vibrate with the old presumably soft or broken mounts....

[svHyLyte]

If that is a stainless steel water-lift muffler that is quite old, one of the seams on the internal baffle may have broken loose allowing it to flap against the case. BTDT.

FWIW...

[NotreVoyage]

Thanks for the replies. I also got some responses direct from the YouTube video. Consensus is nothing to worry about but no real identification, which is understandable from the video sound quality..