Answer:
The minimum percentage of noise level readings within 8 standard deviations of the mean is 98.44%.
Explanation:
When we do not know the shape of the distribution, we use the Chebyshev's Theorem to find the minimum percentage of a measure within k standard deviations of the mean.
This percentage is:

Within 8 standard deviations of the mean
This means that
. So

The minimum percentage of noise level readings within 8 standard deviations of the mean is 98.44%.