A common(ish) problem with Dukes that are not quite running correct.
If your bike is fairly standard then you should be able to get rid of this problem with a bit of fettling at your next service.
My old 748 used to do it a little from time to time...and now my 916SP has started it too...must be me!
See here...
http://www.ducatisportingclub.com/sh...ad.php?t=34305
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