Cordless Drill: Grinding or Squealing Sound

If the bearings become worn it can make a squealing sound or even a grinding noise. Sometimes a seized bearing can make this noise as it will spin inside the housing when seized causing the squealing. To replace a bearing remove the end cap, cover on the housing and the 2 transmission screws securing the transmission to the housing on the side of the drill where the cover is located. Remove the screws securing the cover and pull the cover off. Pull the motor and transmission out of the housing and separate the 2. Remove the armature from the field. Remove the bearing from the armature with a bearing puller. Install the new bearing on to the armature shaft. Reinsert the armature back into the field then reattach it to the transmission and reinstall the transmission/motor assembly back into the housing. Make sure all brush holders and brushes are back in place. Reinstall the cover and the transmission screws securing the transmission to the housing. Reinstall the end cap.

If the gears are starting jam up inside the transmission due to, having a chipped tooth on a gear or missing teeth on one or more of the gears then this can cause a grinding sound coming from inside the drill. To fix this problem you will need to replace the transmission.
Insert the proper screw driver into the drill chuck and snug the chuck up against the screw driver and remove the chuck screw remembering this screw is reversed thread. So turn it clock wise. Next, insert a large allen wrench inside the chuck and tighten the chuck down on it. Hit the allen wrench with a hammer to loosen, or place a pipe over the allen wrench for leverage. Make sure you have the transmission set to the lowest setting before removing the drill chuck and motor. Next, remove all the screws on the cover securing it to the housing as well as the screws securing the transmission clutch assembly. Remove the cover and the transmission clutch assembly. Pull the gear selector switch out and separate the motor from the transmission. The two should just pull apart; you may have to twist a little.

With most models, the planetary gears are visible when you separate them. Inspect the gears for damage. If there is damaged on the gears then replace the transmission. If you can, spin the transmission with your fingers and get a feel and a listen. If you suspect the inner workings are badly replaced. Marry the motor to the new transmission or the old one that you have cleaned out.
Reinstall the gear case and motor back into the housing aligning it up properly to lock into any grooves in the housing. Reinstall the gear selector switch. Reinstall the cover back onto the case making sure all the wires are tucked inside the channels inside the housing. Reinstall the transmission clutch assembly to the case. Snap the brush springs back into place and reinstall the rear cover. Reinstall the drill chuck hand tight. Install the screw back inside the chuck remember it is reverse thread so turn counter clockwise to tighten.