Fix for "whining" speakers

For almost the past year, I've noticed that the left speaker on my MacBook Pro is emitting high-pitched "whines" or buzzing sounds when I play audio over 50% volume.

The problem seems to only happen with audio from videos (Youtube, Netflix etc.), and not really music.

The higher pitched the audio is, the worse the "whines" get; they get more frequent and louder.

So, is the only way to fix this by taking it in for service and getting the speaker repaired/replaced?

It doesn't happen when I listen with headphones, so I am almost certain this is a hardware problem and that it would not be solved with software troubleshooting.

Open to any suggestions though!

For reference:

I have a 13-inch MacBook Pro (no-touchbar) purchased in August 2017; I'm still running High Sierra