Ok, so I put the 675 back together…I oiled the axles, cleaned everything up. I haven’t greased the gears 
Didnt have time to locate it
So, I start running it around the track, and sometimes it makes a horrible screeching noise. Could I have tightened the screws on the drive wheels for the crossbar assemblies too tight? Or do I need to run out to the store before closure today and get some grease quickly?
Check the bearing plate on the opposite side of the armature, you can easily forget to grease it when reassembling it. That will cause a screech. Ive never had driving rods squeal, just squeak intermitently.
I had the same exact problem, using a generous amount of good grease whipped the problem. Don’t hold back on the lubricant. Jake
I’ve found the worst screecher on spur gear motors to be the armature shaft bushings. These bearings see the highest RPM. Give them each a shot of oil. Be careful not to over do it on the motor brush side or you risk getting oil on the comutator face.
my 675 makes that noise when comming out of one turn, but not the others. And I Lube it regularly.