My furnace is 2yrs old. When new I upgraded my filters to the new 3M - Micro filters and the motor started howling/wining/screaming, you know what I'm saying.
I realized that it must be a "high velocity" filter. So I replaced the original one back, that looks like cobwebs.
Then after the sound stopped.
Since then I always replace every 3 months. With same 'useless' filter, not a problem.


Now that it's 2 years old, unserviced, I am hearing the same sound but quieter, inspire of new 'high velocity' filters.


Looks like I'll have to call their 'Stealership' after only 2 years :(
Could the problem be condensate obstruction?

The cheap filters are OK if you change them every 2 months. I wouldn't think the condensate would be causing this problem. What is the size of your return duct?