I think it came from somewhere on the right side of the frame but I can't find where it goes for the life of me.

 

Are you sure it came from the bike? Maybe someone will recognize it but I sure don't... my memory could be slipping though.

Almost looks like an old fashioned hearing aid…?
Sneezles61

The photo needs the proverbial coin next to the part for a size perspective.

I have my DT175B on my lift stripped down to the frame and there was nothing like that on mine.
 

"The photo needs the proverbial coin next to the part for a size perspective."

And maybe close up photos of any numbering/lettering on it. 

I'm pretty certain this came from the bike. When I took it apart, I remember removing it and thinking, "well this part makes sense that it goes here and fits just right. I better remember where it goes." ... And of course here I am posting on the forum because I can't remember. I know it came from the bike. It's the only one I have. I'm pretty sure it's original but not 100%.

 

Maybe it’s part 29 on the diagram below. I don’t know what that part is, and I don’t think my bike had that part on it.
 
 

29 = tool kit.

Ha!  Well like I said, my bike didn’t have that part…
Maybe that rubber piece fits into that small opening where the seat portion of the frame blends into the backbone of the frame, but then why wouldn’t it show up on the parts diagram.