2006 Impala 3.9L - Pulsating Noise in Neutral/Park

My Impala just recently started making this weird pulsating/clunking noise when it's in neutral and park, but not in drive or reverse.

Here's a video where you can hear the sound (taken in the engine compartment with the hood open): https://youtu.be/YBm2DJfWdfY

I don't think it's related, but I'll include it in case it is: the car also recently started to occasionally lurch forward when accelerating. I'll start to accelerate and it will respond normally for a second, then all of a sudden there's a quick, hard jerk forward that feels almost like a car rear-ended me, then it continues accelerating normally.

What could this be?