That's not quite right - the quark-gluon plasma that formed after about a millionth of a second was very much a fluid - it behaved as a nearly frictionless liquid.The Big Bang was neither big nor a bang. It started from a tiny singularity and there was no fluid in existence to carry sound.
Also, the singularity is just the point where general relativity breaks down, it just means we can't say what there was or what was happening at that point, and a measure of size is only relevant with respect to our observable universe, which is a small part of the whole (the default assumption is that the universe is spatially infinite, and was at the big bang). It was not an expansion of a point in space, but an expansion of all space, which may have been infinitely large. Singularities are points in time, not points in space.
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