Chosen Solution
My MacBook Pro is from mid-2012, whenever I play audio or video from left side speaker getting distorted sound.
It sounds like the speaker has failed. Using the Sound control panel try a mono recording of someone speaking sliding the bias between the two speakers (left & right) to be sure it’ the left speaker thats bad. It’s a bit of work as you’ll need to take the logic board out. Here’s the IFIXIT guide: MacBook Pro 15" Unibody Mid 2012 Left Speaker Replacement and here is the part you’ll need: MacBook Pro 15" Unibody (Early 2011 through Mid 2012) Left Speaker - Apple P/N 922-9747
