First of all let's review a second...
Your heater fan is making nasty noises. Almost a grinding sound. So we all assume its a bearing. But maybe its something stuck in the fan? Well, bunky it could be either and we'll try to fix both.
First let's look at the fan as it's installed in the car.
It's held in by a clip at the right end of the motor. A couple of inches ahead of the brushes are a couple of rubber isolated mounts that snap into place. You'll see these in a later pic.
To get to the fan you'll have to remove the plastic covering from the rain tray, unbolt the air duct housings and remove. You may need to get behind the dash to hold the nuts in order to loosen the bolts. Not difficult a bit of a PITA.
Once you have all that out of the way you'll see the fan. There are two power leads from the motor to the resistor. Unclip the resistor from it's clip and undo the connections to the motor.
Once the fan is loose from the car test it for noise by hooking it up and running it. Is it running smooth? Any noise? Hold it horizontal to see if it's noisy. Odds are it sounds fine. I didn't do this step but went ahead and reworked the bushing. That's ok but I probably didn't need to do that.
The majority of the noise is the fan rubbing on the fan housing!!! After fixing my fan and reinstalling it I had plenty of noise. the rubber grommet seen in the following pics had shrunk and the fan was rubbing under the squirrel cage. I manipulated it (that's the same as fiddliin' with it) to see what would make it better. Eventually I put a 5/16" washer under it to raise the fan up out of the way. I mention all of this now so you don't have to disassemble the fan motor unnecessarily.
Don't get me wrong! I'm sure the fan motor could with some lubing anyway but you don't need to take it apart to do that. Use good oil. NO WD-40!!!! Or PBlaster. They're not lubes but solvents!
Now back to our pics. The end on the fan motor has an endcap that holds the brushes and has a bushing holder. That's right BUSHING! Not bearings. This is a very low tech motor. It's hard to believe that after 20 years of use it can even turn but it does.
Inside the endcap is a ring of felt that the bushing turns in.
None of this is terribly difficult to take apart. A little frustrating but not difficult.
The bushing on mine was almost seized to the shaft and was turning only within the felt ring. I removed the bushing with some pliers and proceeded to lube everything liberally. Then I sanded down and polished the shaft so it would turn within the bushing.
Another look at he motor with the brushes removed.
Bushing on shaft (blurry pic)
Bushing in felt ring.
After lubing put it all back together. The front bearing can't be disassembled without removing the fan so don't bother. Drip some oil thru the fan onto the shaft and it'll be ok. Please keep in mind that the fan is sold as a complete unit, no parts are available from VW should you loose anything.
Now check it while out of the car. Make sure it's running ok. If so then start putting it back in. You press down on the back rubber square until it's locked into place. Then you tilt it forward until the grommet is over the peg that positions the front half of the fan. DO NOT CLIP the fan in yet. It is now located well enough to hook up and run it. So do so. See if it's rubbing. You've heard it run when it was free so you can be sure that any new noise is the cage rubbing on the housing. You may have to wiggle it some. Once you're satisfied clip down the end of the fan and repeat testing. Hopefully it all went well.
I've had my fan out and back in several times with no problem with it rubbing. Now all of a sudden I did. That's what made be realize the grommet had worn and was letting the fan drop into the housing.
Last pic. Look at the spot where it's been making a groove.
If you've been letting your fan grind away for a while you won't hurt anything except to wear a groove in the housing. And that will be your tell-tell sign of what's going on. And the fan seems to be the type that once overheated it stops running. Once cooled it runs again so you're ok. Mine never even blew a fuse. Your fan should blow on all 4 speeds but the #4 speed is the only one that does not pass any electricity thru the resistor so use it to test with. Why? So you won't burn your pinkies on the resistor fool!