Why does static noise keep coming from macbook air when I use sound?

I have an Early 2015 Macbook Air Version 10.11.6 OS X El Capitan.

Whenever I play a video with sound or play a song on itunes I start hearing static almost immediately after the video/song starts playing. I have tried to fix this problem by restarting my computer and pressing command + option + P + R. This was effective in stopping the static a month ago when the problem started but now it is just not working at all.

If anyone has any explanations as to why this is happening and/or any solutions to this problem, that would be super helpful and I would appreciate it a lot.

Thank you.