Perkins 4.236m

[NorViking]

Hello, i have a Perkins 4.236M in my boat that makes a strange (blokk fløyte nesten), When the engine is running I get this type of flute sound somewhere in the right side up front on engine and this sound can be mild, or very likely a flute which if you remember old days from school we had these flutes they gave us to play with this destinct sound, and this is exactly what it sounds like. And it just gets louder and louder when I give a specific rpm or trottle. I have tried changed belts, sprayed the belts with sticky belt spray which non of this did anything with the sound. And changed the water pump on engine. New top (head) and gasket, new alternator and lots of other small new parts. And still the sound keeps coming back like a flute. Any thoughts on what this could be?. 

 

Sorry for typing in English, I'll correct and answer in Norwegian to anyone who might come with some input, best hopes a sailor.