So I've begun to notice a reverberation or hum when I lift off my accelerator. There's nothing to feel and it's a low, bassy sound. Akin to driving over rumble strips. But it has me worried about some kind of impending failure. Has anyone heard anything similar in their vehicle? I placed a microphone in the engine bay and near the exhaust, and while difficult to tell in the video, the sound is definitely coming from the engine bay.

Notice the sound isn't present in the first 1:30 of the video although there are several lift offs. (I just realized the sound cannot be heard if played from a phone, make sure you use desktop speakers or reference headphones)

 

I wonder if it's something to do with the symposer, you could try removing the pipe between it and the cabin input. You know what that is I hope.