thud when shifting from first to second on a fairly hard acceleation from a stop

[986Cool]

So when i shift from 1st to second, i get a thud after releasing the clutch and applying accelerator, doing a higher rev shift change...Any ideas as to what this could be a indicator of?...not spinning tires or anything, I don't do that..but what I like to refer to as spirited driving ya know, the "Porsche experience"

Will