If Audyssey detects on any of these it will try to create correction filters for them and this will clearly adversely affect your results. Remember, just because you can't hear the noise doesn't mean that Audyssey can't. If Audyssey detects the noise level is too high, it will raise the level of the chirps and try again. It will do this three times before giving up and displaying the error message. So long as the error message is not displayed, Audyssey will cope with the ambient noise level and deliver a good calibration.
If you get the error message and you have ensured that everything is turned off, you might want to try the calibration later at night when external noise is usually much lower. If you still get the error message despite that, then there is a chance that you have a fault. Often the mic may be faulty or have become damaged. Mics can be damaged by static electricity for example. If this is the case, you will need to obtain the correct replacement for your mic and then try again. If your unit has a factory reset procedure, it may be worth trying that before you blame the mic.
It is worth noting that you do not need to be paranoid about background noise levels. Chris Kyriakakis has stated (Ask Audyssey 14 July 2012) "If you are not getting a noise error then the data collected is perfectly fine." In other words, the calibration is not somehow 'improved' by having a very quiet background noise level. Just keep the noise levels as low as you can when calibrating."
My question is, will you get the same calibration results if there are a few sudden noises (car horn etc) as you would with absolute silence?
To me, parts of these paragraphs contradict themselves as written. It says, "if you are not getting a noise error message then the data is perfectly fine." Then in the first paragraph it states, "If Audyssey detects on any of these it will try to create correction filters for them and this will clearly adversely affect your results."
Why would it create correction filters if the system is designed to re-chirp faulty sessions or show an error message if there is ambient noise present - thus, repeating the process until it goes through.
"The reason we take 10 chirps per speaker is to overcome the effects of transient noise. They will be averaged out if they only happened during one of the chirps."
If the chirps are averaged out, does this mean that 7 clean chirps are averaged out against 3 poor chirp-readings?
"the calibration is not somehow 'improved' by having a very quiet background noise level."
If the 10 chirps are averaged out, then wouldn't it be better to have 10 chirps in silence?
I am just trying to get a consistency about this, as getting a quiet environment is the biggest challenge of Audyssey.