I recently bought a Texas Instruments Program Recorder on eBay. The eBay auction description was somewhat unclear. It said the recorder worked, but it also mentioned that the cassette player was noisy when adjusting the volume. I took the risk and bought it anyway, thinking the tester was probably referring to the speaker which is not important. It turns out the noise occurred when the cassette recorder was sitting flat. It would make a light metallic grinding noise, and it had nothing to do with adjusting the volume. If you held the cassette player on its side or face down, it didn't make any noise.
I decided to open it up to see if I could identify the problem. When you remove the back, you find a circuit board. I had to de-solder two wires going to the microphone to lift this up this circuit board and see what was underneath. There are three wheels connected via a belt. I could see that one wheel was metal and it would drift up and down vertically, on its mounting post. When the player was sitting flat, this wheel would drift down and rub against the metal housing that contains it causing the noise. The housing is attached via a Philips screw which was clearly loose. I simply had to tighten this screw to correctly position the wheel.
Initially, I think I over tightened the Phillips screw. The player started misbehaving where all three buttons FWD, Play, RWD would activate RWD. In trying to repair it, I thought I broke something else. Just to be sure, I reopened everything, and I could see that the metal wheel and a black plastic wheel appeared to be rubbing each other . I loosened the Phillips screw slightly to re-position the metal wheel, and everything is now working perfectly and quietly. I did reattach the microphone wires.
I probably should have taken some pics, but hopefully, I've described my symptoms and solution well enough to help someone else if they ever have this noise. I imagine this could be a common issue with these given the position of the Phillips screw.