I am just installing Big Sur on my brand new MacBook Air, and this very loud fan noise came on. Is this normal?

If this is an M1 MacBook Air, there is no fan in it. If it is an Intel Air, then the Big Sur upgrade is very likely to kick the fan on as it is a very lengthy and demanding installation, and that would be normal. What would be abnormal is after the installation is complete, and the Air was idle and then the fan went nuts.

KPeterzen wrote:

I am just installing Big Sur on my brand new MacBook Air, and this very loud fan noise came on. Is this normal?

Are you experiencing high Energy use (short battery use time)?

How about poor performance?

Generally, all these affects come together. They all (typically) have the same cause.

Have you tried:

• Booting into Safe Mode? (Be patient! This initiates a full drive repair, which can take a while.) This not only repairs any drive issues, it also prevents many third-party kernel and system extensions.
• Creating a new user, and running as this new user, without setting up any login or startup processes?