Very loud "squealing" noise from fan blower for

check with fan closure. If noise continues then it is problem with controller.

Bad blower motor bearing or a bad belt tensioner

As I look at your letter, which is very good, I might add, here are the few things that occurred to me.
The "loud squealing" should be a belt.
You have one or several belts, and if they get loose, or are worn out ( that includes the belt rubber getting old and hard) they will squeal like that.
However, the squealing also may be coming from one of the pulleys the drive belt or belts are attempting to turn.
If you have a bad bearing in one of the pulleys, you can get that loud sound like " a train".
If you are really careful, a "mechanic's stethoscope" might help you.
That is to take a really long screwdriver, and put the tip on each of the pumps or base of each pulley, and the handle end to your ear, and you can hear the bad bearing "scream" with the engine running.
Be blessed.

same problem...not an a/c issue. When the fan is on and when you turn left.sounds like something rubbing in the blower. took the blower off, no obvious blockage.

Sounds like your blower motor bearing is going bad. Pull glovebox and you can access blower motor. Pull blower motor and check that fan/cage is tight and not clogged with leaves etc... Had an instance when mine made a bunch of noise found parking stub had been sucked into fan,

Put some lubricant, oil, WD40, etc. on shaft of fan. Spin the fan with your finger and work the oil into the shaft until the fan spins freely again. Reassemble and problem will be gone for 2-3 weeks. Repeat again until you want to replace the fan motor.

A bad circuit board should not make any noises. A bad solenoid valve could make a loud buzzing noise. If the noise is a squealing noise then you have defective bearings in the blower motor.
If you disconnect the low voltage wiring from the solenoid valve and you still hear the noise, then its not the solenoid valve.

Noise comes and goes sound like metal on metal not a belt squealing

Belts stretch from new. Try to tighten them again. Hopefully the are not glazed or this may stay with you.

What kind of loud noise??  A loud electrical noise??  A loud squealing noise??
It's possible that there is a foreign matter inside the filter chamber jamming up the blower fan.  Pull the filter screen out and look down the filter chamber area and see if there is a sock jamming the fan from turning.  If you can pull it out, that should resolve your problem.  If not, you may need to call a qualified LG technician to resolve this issue.