Sound issues on multiple devices.

hey guys.

---So I'm working at a repair depot for a local service provider, and they recently started selling Moto G 3rd Generations. We got our first batch in a few weeks ago, and ran through our screen replacements, speaker replacements, and soforth. we got about 18 of them back, all with a failing earspeaker issue.

--- We ran the Oxford Speach Test on the earspeakers, and the sound comes out relatively soft. We made sure the speakers were aligned correctly, tried replacing each of the earspeakers with MULTIPLE parts, and I have even jumped the leads to a different model of speaker, and gets the same issue.

--- My first question is, "is this a known issue with this specific model?"

--- My second question is, "is there a known fix to solve this problem?"