Try using the Balance slider to focus audio to one speaker at a time which makes it much easier to detect distorted speakers. Play some audio which you are familiar and know to have a clean sound. Having test audio with a range of frequencies is best (high, med, low) and play the audio slightly louder than normal.
Compare the sound from the internal speakers with headphones or external speakers. If it is the source audio, then headphones & external speakers should also have the issue.
I do know that the 2013 to 2014 and even 2015 MacBook Pros tend to have their speakers fail (usually distorted, but some have very weak/low audio). I haven't noticed any other Macs with speaker issues as that has been extremely rare except for the noted models. I've never seen so many speaker failures in any other Macs in 20 years. I've only encountered a couple of speaker failures with the USB-C models so far with our organization's Macs.
Edit: The Balance slider can be found in the "Output" tab of the Sound System Preferences.