Odds are that it is the rear drum bearing.

Remove the cover at the back of the unit so you can get to the back of the bearing.
Watch out for the ball bearing as they like to take off when released and then play hide and seek,
Then a couple drops of oil to the bearing to se if it is the culprit.
This is just a diagnostic.
If it does help then dismantle the unit and check the bearing parts.
If OK you may only have to re-grease the bearing.
Be sure to use high temperature grease.

You can do the same with a drop or two on the idler wheel shaft.

Check the front drum support glides for wear.

I doubt that the drive belt has stretched.

If you have to take the unit apart this is a good time to check the belt for cracks. Also any other parts that are part of the drum rotation ( drum seals etc.)
Give the interior a good cleaning including the blower wheel.

Since you are working on the unit it is a good time to check/clean your vent system.

Note that the dears parts site has actual part breakdown diagrams that youm may find useful.