  We investigate quantum fluctuations of metric components in coherent 1/2-BPS
bound states of $n_1$ fundamental strings and $n_5$ NS5-branes. The leading
order contribution in an expansion in $1/(n_1n_5)$ is calculated via a
combination of analytical and numerical methods. We find that the fluctuations
are small away from a tiny distance from the source, comparable to the 6d
Planck scale. Comparing this result with an analysis in the literature of
fluctuations in the maximally mixed state, we conclude that the large
fluctuations previously found for the latter are statistical rather than
quantum in nature, and that perturbative string theory provides an accurate
description of these backgrounds.
