Furnace fan intermittent high pitch sound
Sounds more like a bearing going bad to me than a balance issue - unbalance is more often a vibration, and to become unbalanced the fan would either need to have a part fall off, or accumulate crud. 

"Lifetime lubricated bearings" are a standard euphemism for "we prelubed and then provided no way to relube, so when it wears out from lack of lubrication, that's the lifetime of the fan" - i.e. I expect you are looking at replacement. 

I know nothing about your specific furnace, but I know squealing fans pretty well.