There are some switches in the rear of the motor on most of those pumps, as well as a rear motor bearing. Al knows more about them than I do (most of the pumps I've worked on are 5HP or above), but several others know quite a lot as well.

If you can take off the end bell on your particular motor, you might do so. Even if you don't see anything obvious, you can run the pump with the bell off, and see if that allows you to localize the sound better. The capacitor (if present) and switches can be replaced if they are defective.

You can also replace the bearings on the motor, but I've never done that myself.