Mystery Part...help!

That looks like a door stop or buffer of some kind.

 

Possibly a rubber stop for a main/side stand ?
I had one once that detached itself from a Bandit exhaust.

 

Could be from under the hood?

 

You don't say what bike it is, although I think the bike in your little round picture is a Street Twin. Is that right? I have no idea what a Cadillac XT4 is, besides being a car. Cadillacs are a bit thin on the ground here in Blighty and with our petrol prices going through the roof we probably could afford to run one anyway ( I imagine all US cars having 6 or 8 cylinders). However I do own a Street Twin, which I've modded here and there, and I've never seen that part.

 

I was going to have a guess but I’d only say it was something rude, so I won’t.

 

Cadillac XT4 is anew model ? If the car isn't more than a year or so. It could be a part that was never installed !! The worker's on the factory floor get second's to install bits like that !! If they dropped one they just get another one in its place. They don't get time to look or recover it ??

 

Then you disturbed it's hiding place (trunk carpets ?)
And it's finally fallen out...

 

Definitely looks like a bonnet/hood damper. I have vey similar along the side channels

 

Scale is an issue, looks pretty small for a big bonnet or boot? What about the petrol tank filling cover?