Diagnosis
That's a failing drum support roller or idler pulley. The rollers wear out and the metal core grinds against the bracket. A roar points to the blower wheel hitting its housing.
How to Fix It
For a rhythmic thump/grind, it's the rollers. Unplug dryer. Remove the front panel and drum. Inspect the four drum support rollers. Replace any that don't spin freely or have worn-down plastic (part #5304520517). Lubricating them is a temporary fix at best.
If That Didn't Work
A constant roaring is often the blower wheel on the motor shaft. Something has bent the blades or the motor bearings are shot. This requires motor or blower wheel replacement.
Heads Up
Do not run the dryer with this noise. A seized roller can shred the belt or damage the drum. Stop use until repaired.