Learn how your appliance is supposed to operate so you can determine if it is malfunctioning.
A dryer that is operating properly mechanically will be relatively quiet. Clothes buttons slapping on the inside of the drum will make more noise than the blower. Electrical failures make no sound and if they stop the dryer, things get very quiet. Interpreting the unusual sounds coming from your dryer is a very powerful diagnostic aid for isolating mechanical failures.
These sounds come from the two rollers supporting the drum. The bearings are self lubricating to a point and frequently wear out. The roller wheel's inner sleeve bearing has the softest metal and will disintegrate first. The hard metal shaft may not even get scratched. If the dryer is unused for long periods of time, the roller wheel's rubber edge will develop a flat spot which will thump once per revolution.
This is the familiar song of a worn idler pulley. This plastic pulley has a small sleeve bearing that wears out. The idler pulley turns at a high speed and therefore generates a high frequency squeal when it needs replacement. See the above drawing for a picture of the idler pulley.
This is the sound of money and is not a serious problem. Pennies, dimes, nickels and quarters can slide under the plastic baffle in the drum. They will rattle around inside the hollow baffle until they fall through the single hole in the drum and are deposited on the base plate.
All of the information in these Appliance Clinic procedures is provided FREE OF CHARGE. No liability is assumed by the author for the accuracy of the contents or damages caused by the use of these procedures.