I work at a place with LTE GPS trackers on fleet vehicles. Tracking boxes get moved from old -> new vehicles when possible. Otherwise the cell and tracking services are deactivated ASAP to avoid paying a monthly fee on an unused tracker.

I'd personally be equal parts creeped out and curious about the hardware if that showed up on a car I bought. If it's a former fleet vehicle, its probably deactivated.

The particular sound described makes me think of older pre-lte stuff, which in my part of the world was abandoned and became useless a couple years ago.