triton 4m41 engine noise (cicada)

Hi all,

I am experiencing a noise in my 3.2l diesel that sounds allot like a cicada. I have checked all valve clearances and have adjusted to spec.

the motor has 250000km on it but the sound has been evident since i bought it with only 105 000km.

The timing chain tension seemed to look fine to me (which means nothing).

I am aware that these tensioners are prone to failure and I will be replacing.

But while I have the car in the shed, i was hoping some one may be able to assist me with the noise sounding like a cicade.

extra info - I have cleaned intake manifold and EGR parts giving me major power difference but noise remains.

all fan belts have been replaced but noise remains.

valve clearences are to spec.

timing chain has never been replaced and I have not checked the timing or am aware if I need to. (some may laugh at me for this, feel free)