Sounds like you have two problems really. First if you only have high
speed the resistor pack has probably gone bad. This is located in the
blower housing. Second either something has gotten into the housing, or
more likely the motor is failing (brushes worn, bearing worn, etc.). The
blower is behind the glove box. This is truly one of the most annoying
designs to work with that could have been conceived. There are several
bolts (8mm head) two at each side and one or two underneath if I remember
correctly. Then you have to sneak the sides through the opening. The
blower is held in by screws. You could try taking the blower out first to
see if there is anything loose inside the housing. The annoying part comes
when you try to put the glove box back on. First fit it back into the dash
opening, then hold it in position while lining up the bolt holes, position
the side trim strip with your other hand and start the bolts with the
other (third) hand. Not a Tibetan God, well I m not either. Try holding
the bolt on a socket, with the trim strip already hanging on the bolt to
get the first bolt started on each side. Don't tighten anything until
they're all caught. The resister pack is up and to the left about 2 1/2"
square also held by screw.
good luck
douglas