My various P2K locos run smooth and quiet–with the shells off. As soon as I put the shells back on the locos make a quiet hi-rev clicking that was totally absent without the shells on. This is not a thumping sound and the cracked geared axles have all been replaced. These locos have been completely lubed and any old grease removed. I even made sure no wires were touching the flywheels or gears. The clicking matches the rotation speed of the motor, not a lo-rev sound from the wheels.
Maybe the shell is acting as a sound chamber. There are no loose parts on them. Any feedback is greatly appreciated…
You could try putting extra thin foam. The stuff you can see through. That may eliminate the noise. That could work.
If the shell isn’t actually being swiped periodically by a component of the drive, the shell is either not seated properly or it maybe has a tiny fracture/separation someplace. Some reported that the odd BLI tender shell was noisy a few years back. They then reported that things improved considerably if they applied some electrical tape to the sidewall interiors.
Any witness marks on the shell, weight or universals from contact ? Did this occur after you worked on the units or was it present before ?