I am missing several screws for attaching the fan blades to the housing assembly. What thread are they? The length appears to be 7/16"

With a screw driver? And perhaps you also clean all blades. Sorry if you already did that.

It may not be the motors making the noise, but the blade irons that are attached to the motor are loose and are rubbing the housing.

To confirm this, turn the fans OFF. When the blades stop turning, use a step ladder to reach the fan blades and the blade irons. Using a Phillips head screw driver, attempt to tighten each blade iron screw (2 in each iron), that screws into the fan motor spindle. I suspect, you'll find one or more loose. Especially if, the lock washer wasn't installed on each screw.

Hope this helps you solve the problem. If it doesn't, contact Hunter per the instructions in your Owners Manual. As there is a slim chance that there is a manufacturer's defect involved.

For most ceiling exhaust fans, the motor portion is usually attached to a metal housing plate. If this is the case, there is usually a hex or phillips screw on one side or perhaps in a corner which retains the entire housing plate. The motor assembly is usually attached to this plate. Unplug the motor wire inside the fan housing. Remove this retaining screw and look to see if one side can slip downward while the opposite side is usually retained by two metal tabs that are in metal side wall slots. If sliding down the retainer housing is working, then once clear of the metal frame you can pull backward away from the side wall to release the two tabs from their slots. By now you should have the motor assembly and fan blade assembly in your hands ready to dismantle, or clean & lubricate as needed.
Nimsgame

Here some toubleshooting:

Problem 1. Fan will not start.
Probable Cause
1. Fuse or circuit breaker blown.
2. Loose power line connections to the fan, or loose wire connections in the switch housing.
3. Reversing switch in neutral position.

Suggested Remedy
1. Check main and branch circuit fuses or circuit breakers.
2. Check line wire connections to fan and switch wire connections in the switch housing.
3. Make sure reversing switch position is all the way to one side.

WARNING: Make sure main power is turned off.

Problem 2. Fan sounds noisy.
Probable Cause
1. Blades not attached to fan.
2. Loose screws in motor housing.
3. Screws securing fan blade flanges to motor hub are loose.
4. Switch housing binding against the blade hub.
5. Wire connectors inside switch housing rattling.
6. Screws holding blades to flanges are loose.

Suggested Remedy
1. Attach blades to fan before operating.
2. Check to make sure all screws in motor housing are snug (not over-tight).
3. Check to make sure the screws which attach the fan flanges to the motor hub are tight.
4. Check to make sure that the switch housing does not bind against the blade hub.
5. Check to make sure wire connectors in switch housing are not rattling against each other or against the interior wall of the witch housing.
6. Tighten screws securely.

WARNING: Make sure main power is turned off.

Problem 3. Fan wobbles
Probable Cause
1. Setscrew in motor coupling is loose.
2. Setscrew in the hanger ball/downrod assembly is loose.
3. Screws securing fan blade flanges to motor hub are loose.
4. Fan blade flanges not seated properly.
5. Hanger bracket and/or outlet box is not securely fastened.
6. Fan blades could be out of balance.

Suggested Remedy
1. Tighten the setscrew in the motor coupling.
2. Tighten the setscrew in the hanger ball/downrod assembly.
3. Check to be sure screws which attach the fan blade to motor hub are tight.
4. Check to be sure the fan blade flanges seat firmly and uniformly to the surface of the motor hub. If flanges are seated incorrectly, loosen the flange screws and retighten.
5. Tighten the hanger bracket screws to the outlet box, and/or secure outlet box.
6. Interchanging an adjacent (side-by-side) blade pair can redistribute the weight and result in smoother operation.

WARNING: FOR YOUR OWN SAFETY TURN OFF POWER AT FUSE BOX OR CIRCUIT BREAKER BEFORE TROUBLESHOOTING YOUR FAN!!!

Hope helps.

In order to replace the fan you will buy a 2 or three piece lexan fan kit containing the fan a spacer and shaft.
You must remove the carpet head and then looking from the back of the machine you will find a series of philips screws on the outer edge of the fan housing facing towards the front, several of which may be partly covered by the motor housing. You will remove the forward facing screws to allow the housing to separate and reveal the fan.
If you are lucky there will be a sideways hole through the impeller shaft allowing you to slip a nail through to help twist the saft to unscrew it while holding the fan .
The shaft will turn off revealing a threaded motor shaft with spacers which the broken fan will slide off revealing a second spacer at the back . Be sure to replace these spacers in the same order when re-assembling the unit. Secure the shaft hand tight. Post back to advise if you need further help

How do I clean my Cyclone or Air Companion™?
Lay the fan face up on a flat surface. The front grill should be facing you. Remove the screws from the rear grill. Place a flat-head screwdriver into the gap between the front and rear grills. Pull the front grill towards you, exposing the fan blade. Do not remove the knobs on either side. Then, wipe the blade with a soft, damp cloth. Use a mild detergent if necessary. Be sure not to touch the motor. Click here to download product instruction sheet.

Drawing REF: http://www.ereplacementparts.com/bosch-3107dvs-0603310639-random-orbit-sander-parts-c-128_1044_1230.html

To remove the Dust Fan/Coupling Assy. I did the following: I disassembled the plastic housing, removed the Backing Pad Pos. 733 and Dampening Ring Pos. 51.

It seems the Star Washer Pos. 29 holds Bearing Pos. 30. onto the armature shaft and the Coupling Pos. 27 seems to be stuck in Bearing Pos.29. I used a 30mm long M7 hex-head bolt and 11mm ratchet turning clockwise (std RH thread) to pull the Coupling and Star Washer off. Luckily, there was enough thread left in the coupling to do this gear-pulling action with the longer bolt.

To remove the rest of the Fan Assembly I removed the 2 screws Pos. 43 holding the Brush Holder Assembly, Noted the position and removed the Spring Clip Pos. 32, then removed the Armature w/ Fan and Dust Fan/Coupling Assemblies. Firmly gripping the armature I was able to remove the Dust Fan from the armature by turning it clockwise (LH Thread).

Now that I have removed the parts and believe I will be able to reassemble them, I have ordered a new Dust Fan/Coupling Assembly.

I hope this helps someone else having a similar problem.

4.9L SFI
SPECIAL SERVICE TOOL(S) REQUIRED Description Tool Number Fan Clutch Holding Tool T84T-6312-C Fan Clutch Nut Wrench T93T-6312-B
Removal

1. CAUTION: The large clutch assembly nut has a right-hand thread and must be rotated counterclockwise to remove it.
   Remove the fan clutch (8A616) from the water pump (8501) by turning the large nut, which is part of the fan clutch, using Fan Clutch Holding Tool T84T-6312-C and Fan Clutch Nut Wrench T93T-6312-B.
   

1. Remove two screws retaining fan shroud.
   

1. Remove the fan blade (8600), fan clutch and shroud.
   

1. If the fan blade and fan clutch have to be separated, remove the remaining bolts attaching the fan blade to the fan clutch
   

5.0L, 5.8L and 7.5L Engines
Removal

1. Remove screws retaining fan shroud (8146) to radiator (8005).
   

1. Remove four screws retaining clutch on water pump hub.
   

1. Pull fan clutch and fan blade off water pump pilot and remove fan clutch, fan blade and shroud from vehicle.
   

1. Remove four screws and separate fan clutch from fan blade.
   

Item Part Number Description 1 8509 Water Pump Pulley 2 57632-S Screw and Washer Assembly, 5/16-18 x .62 Hex 3 8600 Fan Blade (5.0 and 5.8L) 4 8600 Fan Blade (7.5L) 5 8A616 Fan Clutch 6 380288-S2 Screw and Washer Assembly, 5/16-24 x .88 Hex A — 16-24 Nm (12-18 Lb-Ft)