Unless it's a really new motor it likely needs to be greased.
Look for a grease port on each end of the motor. The first picture attached motor on a Free Westinghouse Type J, you can see the hole in the housing that, I think, has a wick material in it; I squeeze grease into the hole until it comes out. The second picture is a Kenmore 117.552 motor and there is a housing on each end that will actually unscrew and has a wick in a spring that is filled with grease.
If the wicking material is too old and gets too dry or maybe brittle it might have to be replaced, if you can find it and figure out how.
What you use to grease it is an entirely different discussion. From my reading the grease goes in solid, more or less, and then the heat of the motor spinning melts it and lubricates, therefore the type of grease depends on its melting point. Lots of discussions about this, what to use and what not to use, although I have not searched this forum for information.
Sorry for the blurry pictures, cheap phone.