I just had a staff member ask me if white noise is banned in childcare centres. this is not something I've heard of as being a risk to children. could you please clarify?

The use (or non-use) of white noise or relaxing music is not a specific part of the Red Nose Safe Sleep Recommendations.
https://rednose.org.au/article/red-nose-safe-sleeping-recommendations

Maybe this has come from your local regulatory authority?
I’m sure ACECQA would have notified all services with updates on website information if white noise machines were banned. (eg like they did with bassinets in 2023)
https://www.acecqa.gov.au/resources/supporting-materials/infosheet/safe-sleep-and-rest-practices

Some concerns that have been generally expressed by other Health & Safety Organizations, about the use of white noise in the home & in child care & these include basic safety information eg battery security, sound volume & use of power cables & their risk to baby.
Product Safety Australia (ACCC) & Kidsafe may also be used as reference points for parents/Child Care, also referred to in the info sheet from ACECQA (linked above)