Here, you had a new employee who had an ‘invisible’ disability – a hearing impediment that would not have been apparent had he not mentioned it to me (he wore no obvious hearing aid).  His disability conflicted with his ability to perform his job due to the environment he was being required to work in.
That music wafting in the air?   While perhaps not an issue for non-hearing impaired employees, it clearly was an issue for this employee.  So much an issue that he felt it necessary to alter how he was doing his job, from leaning in to hear customers to going so far as to disclosing to them the fact he was ‘hard of hearing’. 

Read more at
http://www.aoda.ca/?p=883