First thing I did was check all of the above, except blockatge of the main drain. Too cold to get down there w/o a wet suit.

My designated sheer descent pump is a little noisier than the others (same brand & size). Nothing that sounds horrible or something mechanically wrong, it's just more of a lower humming than the other two (especially at start-up), which wasn't the case before the problem occurred.

Thanks for all of the above help and I'll let you know if I find something in the drain.

Merry Christmas & a happy New Year to all.