Rear Speakers - Sound issues
My macbook sounds noisy and unclear. But, on head phones it very good. Will it be a hardware issue? or could it be software related?
Did someone spill a drink into the keyboard? I've had a few systems which had soda spilled which with the dust from the fan messed them up.
I would start by doing a good job cleaning up the dust within the system and replace the speaker. If something did get spilled you'll need to clean it up as well.