It's extremely hard to describe but IMO sounds more hollow than metallic. I'll try and get a recording but I seriously doubt I'll be able to capture it. Think of a bubble popping but deeper/muffled and louder.

I can definitely feel something when the pop occurs in my left foot. Seems to be when the car "jerks" but only at a certain speed/acceleration combo. Could be me trying to justify the idea that it's an engine mount issue but I don't get the vibration/rattles which supposedly come with blown/worn engine mounts.

FWIW I've disconnected the battery for an hour and reconnected; didn't help.