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I actually found the audio annoying and ended up permanently suppressing it by cutting out a space in some sound deadening foam and placing the unit in that.
Before doing that the audio was only really audible when stationary with the unit under the seat, once moving you would struggle to hear it.
As I could only hear it when stationary, it became annoying when someone walked past the rear of the bike or someone came up slowly beside you when stopped.
For me, the red led warning is enough and I didn’t try any other placement of the unit.