I did server dust cleanup last Saturday. After that, it starts working loudly.

I quickly search for similar topics
https://www.dell.com/community/Rack-Servers/Expected-fan-speeds-for-an-idling-PowerEdge-R540/td-p/6046680
https://www.dell.com/community/PowerEdge-Hardware-General/R930-server-is-making-too-much-noise/td-p/5151057 but without any useful solution for my case.

Also, https://dl.dell.com/topicspdf/poweredge-r540_owners-manual_en-us.pdf p. 44-46

https://dl.dell.com/topicspdf/troubleshootingguide_en-us.pdf p. 90

https://i.dell.com/sites/csdocuments/Shared-Content_data-Sheets_Documents/en/us/poweredge-r540-technical-guide.pdf p. 37-38 didn't help.

Any ideas on how to manage fan noise levels?

BIOS is 2.10.2 as of right now. Planed an update to the 2.11.2 version tonight.