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"hwm54112" wrote in message
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It's impossible for the two to be directly related. If you have no
poltergeist, I would look for a drop in city water pressure (ask
neighbors) and/or debris at the main water cut-off. If even a single
valve has normal pressure, neither of the three suggestions so far is
at issue

At first look it would seem you are correct, but stop and thing about the
situation. The water pressure was exerting force into the clogged drain.
As the clog moved, it may have broken free, thus instantly lowering
pressure, then stopped and rained it again. The OP said he heard all sorts
of hammering. That may have been enough to cause damage to a diaphragm in a
regulator or backflow preventor.