67 C10 Pinging Sound

[IndifferentJester]

Need help resolving some recent problems that poped up. While I was deployed my truck sat and wasn't started at all. New problem arise is that I have a tranny oil leak somewhere and a new pinging sound. At first I couldn't figure out why it wouldn't shift into gear (automatic) and she sounded fine. After finding out that she needed some tranny fluid I topped her off and then all of a sudden the pinging started. It seems to only ping while in park or reverse, not in drive. I'm generally savvy when it comes to fixing my cars but I'm at a loss for this one. I notice a flare in the exhaust manifold (at the end of the video) and know that's not normal at all. Hopefully these are two separate issues and that it's not a tranny problem.

The pinging sound doesn't sound like an engine knock that I'm familiar with and dealt with in the past on a different car. Thank for the advice/help.

https://youtu.be/tQ2JPRMi8kQ