I think mine did that when new but it soon disappears. It may still be there a bit, but if it is it's too low now too hear w/o listening for it. Don't know what it is but probably something to do with the valve train. Maybe the chain rubbing against the tensioner or such. One thing everyone will tell you about the Tbird tho is that when new they make a ton of weird noises and they all go away eventually. Mine sounded like a bucket of bolts at first and now is quiet. the only thing you need to do anything about is a chirping sound when moving, mainly under acceleration. Thats the belt being too loose and it seems to be common with new birds as the belts stretches when new. Mine did that from new. i adjusted it and it went away for a few weeks then returned. I adjusted it a 2nd time and it never returned. they just need time for their initial stretching out.