In Junkyard, you can find a pair of cardboard boxes sitting in a high-up room.
Start out by getting to the 8th checkpoint, immediately after the low pipes that you have to pass under. Go off of the ramp and, rather than dropping down, try to land on the small ledge created by the ramp in front of you. Drive up and around the ramp and you should hit a booster. Fly upwards and turn right, entering a high passage.
When you get up top, slowly approach the standing platform and it will fall over. Drive over and the camera should pan in to show you a close-up of some carboard boxes sitting on a circular stand.
If you go a little further forward, you'll be taken out by some flying I beams, which is actually pretty cool to watch.
So far, the purpose of the cardboard boxes remains unknown. There appears to be a numerical code on the box that could possibly lead us to its content. We can see there is ducktape across the box covering a part of the upper numerical line.The box on the left is thought to be a replica of the 'Tannen's Magic Mystery Box' as seen in this video:
This section is reserved for Confirmation/comments about this investigation. Investigations will remain open until advised by Redlynx that the final solution for each secret is found.