Strange metallic noise / rattle at low rpm uphill

I feel like the noise was present slightly when I bought the car 1.5 years ago (at very low levels though). I recently went on a trip where I bottomed out once on a dirt road and now I feel like it may be louder. I have a CAT shield installed and originally thought it may be that or the 'natural' sound of the clutch switching from battery power to ICE power. The noise tends to occur at about 20% into the ICE side of the power meter and disappears as I apply more throttle/power.

Here is a clip where you can hear the onset of the noise:

Does anyone have an idea what may be going on?

 

After over a year...finally got it up off the ground. It was a damper that broke away from the exhaust pipe. They were grinding against each other at low rpms when the ICE was running:


My fix - a hose clamp sawed down to size off an old piece of dryer ventilation ducting:


Welding would have been ideal, but it seems to be quiet for now.