95 blazer clicking noise in drive and park

I've got a 95 blazer I just bought. I've got paper work stating that the engine was rebuilt last year. I've been hearing a clicking sound coming from the bottom of the front end but it only happens when it's in (over)drive or park (coming from overdrive). In reverse or park coming from reverse the noise stops. any ideas?

Thanks

More detail about the sound would sure help.
Check your driveshaft U-joints.