If you have a Harbor Freight in your area, stop by and purchase an automotive stethoscope. Invaluable tool for diagnosing bearing failure in accessories, problems with injectors, valves, all the little ticking, grinding, groaning that is hard to track down. The screwdriver technique works good, but the stethoscope works better.

On special for $1.99, you will spend more on gas to get there:

Stethoscope at Harbor Freight