Sounds like it might be a dry bearing
Especially if it's worse in cold weather - the bearing squeals until the friction makes it hot enough to make some remaining bit of lube run onto it. <g>
Why not pull it out and oil both ends of the shaft? At the shaft end you can either pull the wheel or squirt oil messily under it and onto the shaft while turning the shaft to help the oil flow in.
And on the end opposite the shaft there is usually a bulge which you can drill a 1/8" 'oil hole' into. Try to make the hole where it will be on top with the motor re-installed in the car. Repeatedly fill both ends with oil - often there is a felt wicking surrounding the the bearings - originally wet with oil - but perhaps now dried out.
Although replacement blower motors are generally cheap enough that unless you are willing to experiment - maybe just replace it?
If it was relatively easy to get out I would try re-oiling it I think. If it was a PITA to get out - I would replace it. But I do love the 'cheating the system' (so to speak) 'feel' of doing things like "just oiling it". <g>
PHM
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What kind of loud noise do you have? Squealing? Grinding? Crunching? A bearing noise or . . . maybe something caught in the blower wheel? A leaf? A plastic bag or candy wrapper? Etc.?
PHM
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It is a squealing noise that continues for some minutes. Sometimes if you just bear with it, it goes away, but lately I just live without the heat on, which is difficult in Chicago this time of year.[/QUOTE]