I removed the front panel of the dryer to inspect, and found that the blower wheel wasn't tight on its shaft. Removed the blower wheel, cleaned the area, and saw signs that the fan had been wobbling and had scraped against the housing. Replacement of the part was a simple job -- aided by looking at YouTube for others' experience with it. This job required 1/4 and 5/16 nut drivers and small snap ring pliers. I had these tools, but if I had not had them I would have needed to get them. Also required was a vacuum cleaner to clean up the accumulated lint inside the dryer.