Flywheel rattle?

[e21Mark]

We're building an E21 BMW and have fitted a low mileage M52/2.8 engine, on Jenvey ITB's, six branch and running DTA Pro 90.

We have fitted a lightened billet steel flywheel, that are dynamically balanced to 20000rpm, but there is a noticeable resonating noise / rattle on overrun. The gearbox is known to be in good order and the clutch is a new, uprated item from AP.

I've been told that a certain amount of chatter, from using a significantly lighter flywheel, is quite common? I've no experience of this myself though, hence my question. Has anyone else had similar issues when fitting a lightened flywheel, or can explain potential reasons for the resonance?

Thanks in advance.

[e21Mark]

Thanks guys.

Sadly the resonating noise remains with clutch depressed. It seems odd that it only happens on overrun though?