Why would it hurt to hold a piece of metal (not hot or cold, but similar to a feeling of aluminum in the mouth, but in the body)?

Not sure. I would suspect it wouldn’t have anything to do with the metal itself. Maybe something on it? Maybe you just got dizzy or something from bending down?

Way too many possibilities and not nearly enough info.

Interdimensional troll transmission.

Yes, probably coincidence. The pain, unique and isolated to whatever physical condition your body experienced came just at the same time you touched that metal. Or else, you might be an X-man and you just discovered your Achilles heel! : )

I wish someone could explain this.
That biting into tinfoil feeling is similar to what I have felt during an MS “Attack” except on a larger scale where it immoblized me.
Has this ever happened to you again?

Did you only touch the bumper once? If so Id say coincidence, but if you touched it multiple times with the same reaction happening there may be somethin there.

Could it have been radioactive?

I touched the bumper twice about 5 minutes apart. Both times a shaky, aluminum-in-the-mouth kind of pain all over my arms and legs.