It started after my short block swap. It happens when the car is put in Reverse, or Drive. It only happens with a mild amount of pressure on the gas peddle in D, but if I'm very soft, it won't make the noise. Every time I put it into reverse (like the video), it makes it.

Thanks guys

 

no one? :/

 

The frequency it's at is roughly engine speed so something that's rotating is rubbing. IF it was just an exhaust pipe rubbing it would make one solid clunk, but this has a definite frequency to it. My mom's plymouth made a sound like that once and it turned out that the dealer that had replaced the transmission hadn't tightened the bolts that hold the transmission to the motor and the torque converter was rubbing against the bellhousing. I'd crawl under the car and make sure everything's tight. Also, have someone start the car and put it in reverse while you've got the hood up and look with a flashlight and see if you can pinpoint the source of the problem. It's definitely something thats rotating rubbing against something else judging by the frequency.