The bass on my MacBook Pro is distorted. How do I fix this.

Sounds like the laptop has a bad speaker. Have Apple or an Apple Authorized Service Provider examine the laptop to provide you with a repair estimate. If you have an older 2015 or earlier model, then the speakers are not that expensive (labor will cost more), but if you have a USB-C model from 2016+, then that will be an expensive repair since the speakers are part of the Top Case Assembly which includes the Keyboard, Trackpad, and Battery.