Ryo wrote:

The reception of my favorite FM stations has markedly degrade
recently. I've been wondering why. Today, I realized one of
my two radio receivers was receiving a different FM station
at the same frequency while the other receiver was receiving
my favorite station. Both receptions were very bad (noisy).
Eventually, the second receiver switched back to my favorite
station and the receptions of both receivers improved.


It sounds like your FM band got enhanced propagation and your first receiver
was picking up a station some distance away. FM receivers have what is
called capture effect if a signal is strong enough it will capture the
receiver despite there being other signals on the same frequency. Since
the other signal went away most likely the enhanced propagation declined
and you got your normal signals.