Trane blower gives tinny raspy noise on high speed

I have a Trane 2 stage gas furnace connected to a heat pump and it is about 12 years old. For the last couple of months we have had a tinny-raspy noise when running in HEAT or in COOL mode. If the fan is turned on manually there is no noise. So today I took the blower unit out and cleaned the entire assembly (housing, squirrel cage unit and motor). They were a little dusty but not bad for the time installed. I took the motor apart, oiling the sleeve bearings and then reassembled the entire unit and reinstalled it. The motor is a 4-speed unit. Further diagnosing it, it would run on low speed when manually turning on the fan. Swapping the low-speed and high-speed it then would make the noise when manually turning on the fan. Calling a motor repair shop I use they said they doubt it to be the motor, but they would guess it to be the squirrel cage itself. They said that the cage will loosen up when the "fins" are crimped together to make the assembly and will cause noise and could well be speed sensitive. What is your opinion? Can I silver solder all points and save a little, or should I buy new?