I'll leave it for Bob to comment on what CASA may want to see in the answer .. and forget "advised" .. your employer is obligated to provide, and require you to wear, hearing protection due to the typical SPL values in and around aircraft.
Hearing protection is super important for pilots. In the bad old days (ie when I came through the system) there was little attention paid to the subject with the result that most of us older folk have varying levels of hearing loss associated with our flying histories. You don't want to repeat the foolishness of the past ..
The linked documents are worth a read, for your background information, regardless of what the exam syllabus might have to say.
(a)
www.safeworkaustralia.gov.au/sites/swa/a...HSC2009-2004_PDF.pdf
(b)
www.safeworkaustralia.gov.au/sites/SWA/a...earing_Loss_Work.pdf
(c)
www.defence.gov.au/aircraftnoise/_Master...aircraft%20noise.pdf
(d)
bib.irb.hr/datoteka/482262.EAA-EUROREGIO-173.pdf.pdf
(e)
www.worksafe.qld.gov.au/__data/assets/pd...earpro_selection.pdf
In general, if you are working in an environment with sound levels up around 80dB(A) or more you need to be using hearing protection. What this means in practical terms, if you are working at a reasonably busy GA or airline airport, you need to have hearing protection on the apron and in flight generally.
Caveat - you can over protect to the point where you can't hear, for example, warnings etc. It follows that your employer has to obtain quantitative data to select suitable protection.
Me, if I were starting out again .. I'd have Class 5 protection on from when I went onto the apron until I came in from the apron at the end of the flight duty period.