OMG...Lifter tapping??

did u do the tranny or a shop. If it didn't rattle before the tranny job...they may of "stressed" it on a test ride. If You did it and right after the tranny work it rattles..check Your oil level first. ( I know it sounds simple but somtimes the obvious is behind somthing)

I would suspect an exhaust leak if happening just after the tranny as the exhaust would get moved to change the tranny

I should read all the posts before adding My 2 cents. LOL