I had the same problem with 2 Macs, the solution was to clean the grille with a dry/clean toothbrush. The issue was that the micro-holes were blocked, which can be confirmed by passing light through them.
I could diagnose the problem by connecting the speaker without installing it, I leave it carefully hanging and it sound really loud.
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I attach a photo of the blocked micro-holes.[br]
[image|3063051]
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