Why is the audio for the speaker & headphone jack low/crackling?

The audio for both the speaker and headphone jack are terrible on my Gameboy but in different ways:

Speakers: Very low, even with the volume wheel turned all the way up. It’s also very crackly sounding (for lack of better words).

Headphone Jack: The volume wheel works as it should through the headphones, but there is an ever present and incredibly loud crackling noise that accompanies the audio, regardless of what volume I have the Gameboy turned up/down to.

Why is this happening and how should I go about repairing this myself?