Anyone know what this noise is?

So I keep having this noise/vibration happen to me between 20-30 mph. I have to be holding at a steady speed. In the video I go to 30 mph, hold (sound appears), then let off the gas (sound stutters and disappears). I have looked under the truck for anything "odd" but haven't had the chance to go under and start rattling things.

It doesn't always happen. This morning it happened but tonight it didn't. However it happens more often than it doesn't.

2011 Tacoma M/T 4 cyl and close to 50k. The maintenance light is on because I forgot to reset it after my last oil change.

https://youtu.be/1Yad8od4Qrk

 

Bump, going out to look under the truck right now