Is $600 to clean a furnace blower wheel a fair price?

I was offered a free unit inspection from a local HVAC company, which identified my furnace blower wheel as dirty and causing stress on the heat exchanger. I couldn't afford their $600 cleaning quote, so I cleaned it myself. After cleaning, the unit now produces a constant harmonic hum throughout the house when the blower is on. I've checked the wheel seating, motor mounting, and housing security. I've also ruled out collision with the wheel. I was able to slightly reduce the sound by reseating the wheel differently, but it's still noticeable and driving me insane, especially since it's winter. My furnace model is PG8MAA036110AFJA (model PG8MAA036110, series F, serial 0614A21968).