Here is your parts breakdown
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Sometimes there is an access panel at the back and you can squirt in some oil. Do not go crazy with it as you are in the middle of your heating elements also you do not want to end up with oil on your clothes. Only do this if it is driving you crazy, it is just a temporary fix.

Best to tear the whole thing apart. You can then check the ball etc. for wear and also remove the old dried up grease. One thing to watch out for is the little grounding ball bearing. It is a frisky little beggar and loves to run across the floor and hide, once released. Use a high temp grease. Car wheel bearing grease or they do have a tube of it on the above. Again do not go crazy with it.

While you have it open check the belt, front glide, idler wheel and drum felt seal etc.. Replace or clean as necessary.

Also give it a good cleaning including the blower wheel.
Would also clean/check the vent system.

Basically an overhaul