Odd Sound From Auto Box while engine idling.

Never had a problem with the automatic transmission till yesterday.

While getting the Cabrio out for wash, when I started the engine and selector was in Neutral, there was a rattling noise from the transmission side. Open the bonnet to look while engine was running, deffo coming from the autobox housing on the flywheel side, could not see any chaffing of anything and noting in on contact with the casing. When I slightly rev the engine from 1000 and above noise goes away. Any suggestions ?

if its not been done recent i would drop the box oil and replace the filter, easy thing to try that fixes most auto box issues. if that doesnt help i would think perhaps the auto box bearing in the crankshaft has gone, but im no expert on them im afraid!