The good people at Lindstrand Motorsports have helped me identify the mysterious noises I thought I was hearing. The noises were real, and they were the result of worn wheel bearings. The left rear wheel can be moved about 1/8" up and down, although it is still tight side to side.
The left rear wheel on a formula car is typically the most heavily loaded wheel in road racing. Road racing courses are generally run clockwise, which emphasizes right hand turns. Turning right transfers weight to the outside wheels (the left side), and the rear of the car is heavier than the front, both because of static weight distribution and because weight transfers to the rear wheels under acceleration. I won't speculate on what percentage of the car's weight is carried by the left rear wheel in a right hand turn, but I wouldn't be surprised if it was more than half. This is the same force that ate up the VW wheel hubs I used a couple of years ago.
What appears to have happened is the outer race of the bearing has become egg-shaped (pointy end up) from the extra weight it has been carrying. It hasn't just generally worn out, which would cause the wheel to be loose in every direction. If you put one hand on the tire at 3 o'clock and your other hand at 9 o'clock and push and pull, you won't feel any play. But put your hands at 6 o'clock and 12 o'clock and you can move the wheel up and down with an audible clunk.
The plan for the next few days is to take the upright off tonight so that I can deliver it (and two new bearings) to LMI tomorrow, as Bruce has offered to stay in the shop after hours to help press the old bearings out and install the new ones. Depending on the hour when I get home Thursday night, I may try to get the car back together that night so I can load up Friday night and head to the track Saturday morning. I don't know if I'll make it in time for the first practice session in the morning, but I should be ready for qualifying in the afternoon.
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If you're wondering why road courses are run clockwise when ovals are run counterclockwise, here's the scoop.
Sports car racing is a primarily British invention (sorry, France and Italy). Brits drive on the left side of the road and put the driver on the right side of the car. That makes right turns easier (the driver is closer to the inside curb, making distance to the apex easier to judge) as well as faster (the driver's weight is on the inside of the car, countering the effects of weight transferring to the outside wheels).
Oval racing is an American invention. Americans sit on the left side of the car, so the opposite conditions to British cars exist.
Road racers trace their roots back to the British sports car drivers. Most "roval" tracks (where a road course uses part of an oval track) are even run clockwise on the oval portion.
The one notable exception is the Japanese Suzuka circuit, which was designed to have an equal number of left and right turns. It is actually a figure-8 layout, with the "back" section built on an overpass to cross over the "front" section.
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