It used to be part of the studio, the section with the dancing cars for Fast and Furious. It's between the picture cars and the Jurassic stuff.
I'm pretty skeptical of what Jsland is trying to imply here. He talks over the clip in the video, so we can't hear what sounds he's referring to and he doesn't describe them at all, and this is the best image of the "vehicle" that he sees inside the area.
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Those look more like cart wheels to me than wheels for a proper vehicle, even too small for a golf cart. Universal uses that space for storage since it's so big and largely unused. I suppose it's
possible that they're doing something in there,
maybe ahead of the 60th anniversary of the Studio Tour, but without any more information, this seems like a pretty big leap to say that anything big is happening in there. My best guess? They're using the space to paint stuff for the park where it's out in the open (so not having to worry about ventilation) but also out of the way of guests/studio operations.