"Lyra thought she could even hear them"

There is little scientific evidence for the Aurora producing an audible noise – the atmosphere is so thin that sound waves would not be carry, and the Aurora itself is so far away that it would take sound waves 5 minutes to reach us.

However, there are several reports of people hearing, as Lyra does, a "swooshing" sound when viewing the aurora. There is a very interesting paper here which investigates the subject more thoroughly.