Stand up, freewheel.. bounce the suspension. Noise...
Sit down, hands off bars, bounce the suspension. Noise..
Feet off pedals, bounce suspension. Noise...
Take bottle out of cage, bounce suspension. Noise...
Hold cables, make sure they are not the issue.
Bounce lightly. Noise... may be suspension linkages or bearings.
If at any point for example, feet off pedals... means there is an issue with BB, Pedals, Chainring, chainring bolts... eliminate the issue in stages.
Its not really that hard... but fucking annoying.
I'm a silent bike bloke.