Rattle / tapping when dropping to idle (video link included)

[Greeney887]

Full Forged 4efte
Upgraded valve springs
Lapped valves
MLS Gasket

Ive got an engine rattle at idle and I cant for the life of me figure out what it is. The rattle happens as the engine drops down to idle when revving up stationary around the 1000-1500 rpm range, the noise is apparent no matter if the engine is hot or cold.

Link to the noise here (im slightly blipping the throttle in the video) : https://www.youtube.com/shorts/lYK-SU07Lyk

Things I've ruled out are

Idle control valve as it doesn't have one
Cam gear tensioner is tensioned
Big ends/ mains just had a full new set of ACL's
Valve shims / clearances are fine (although I wouldn't expect this to cause the noise as it doesn't increase with rpm)
Piston slap (You can hear the piston slap on cold start and its more of a dull thudding that goes away when its warmed up)
Cranks in manifold its brand new

Ive had a poke around with a long screw driver to my ear and its a bit difficult to distinguish where its coming from but ive come to the conclusion that its coming from the gearbox side of the engine.

Any help would be appreciated as Its driving me up the wall

 

[gorganl2000]

if you suspect something in the gearbox,,,try pressing the clutch pedal when its idling and see if it the noise is still there

i'm not sure if you can spot a light in the gearbox from the fork rubber or under the car if the gearbox plate has a cut out in it.. remember to be very careful around moving parts

i've heard some injectors make clicking sounds,,but your noise is a bit inconsistent,,nonetheless, you can check around those as well

 

[Greeney887]

if you suspect something in the gearbox,,,try pressing the clutch pedal when its idling and see if it the noise is still there

i'm not sure if you can spot a light in the gearbox from the fork rubber or under the car if the gearbox plate has a cut out in it.. remember to be very careful around moving parts

i've heard some injectors make clicking sounds,,but your noise is a bit inconsistent,,nonetheless, you can check around those as well

Yes that’s another thing I forgot to mention that I’d checked pressing the clutch in makes no difference to the noise either unfortunately, although I’m not ruling clutch/flywheel/ gearbox out just yet

 

[daniel_g]

The plate between the engine and the flywheel can make a horrible noise if it is bent or making contact.

 

[dac69er]

Could just be something rattling and that rpm is the point where the harmonics are just right to make it vibrate.
Check the sandwich plate between the box and engine has a bolt in it at the bottom as that can rattle if not.

I would also be a bit concerned about your piston slap sounding like a dull thudding. Piston slap is normally a similar sound to valvetrain noise.

Have you confirmed your actual oil pressure?

 

[Greeney887]

Could just be something rattling and that rpm is the point where the harmonics are just right to make it vibrate.
Check the sandwich plate between the box and engine has a bolt in it at the bottom as that can rattle if not.

I would also be a bit concerned about your piston slap sounding like a dull thudding. Piston slap is normally a similar sound to valvetrain noise.

Have you confirmed your actual oil pressure?

I’ve checked that sandwich plate it seems tight although it is bent and all over the place, I just can’t see it coming from there it sounds a lot more internal. Proper check of Oil pressure is next step. I only have the dash light to go off at the minute. Could maybe be a drop in oil pressure slightly as it drops to idle? I’m running 5w40 synthetic oil