I can't say I ever heard brushes squeak on any of my routers, if a bearing is damaged it tends to squeak once it heats up under stress. Shut it down open it up and clean the brushes gives it time to cool down and shrink. If you haven't already, start it up and route something to put it back under stress and heat it up.
With all the stuff I routed over the yrs. I say I ever "heard" bearings squeak. I did junk a PC690 back in 05 from routing composite decking, flakes melted on armature. It was cheaper to buy a new one.
I still have my 1st router Craftsman 315.17480, (haven't used for about 25 yrs) it became louder and seemed to be vibrating more in the early 90s, I believe that's when the bearings began to falter.
The cape is a moist place and I didn't have a dehumidifier in the shop till the mid to late 90s. I believe the tool degrades faster from non use, dust build up and high moisture, if it's used regularly the moisture is drawn out and the dust cooks or is blown away.
Never bite the hand that looks dirty!
The more you know the more you're worth