Hi Dan, thanks for the reply, I do have bullnose on the front edge, for every tread, I cut a 1/2 strip from the same tread board and glued it back to make a square bullnose, see attached photo here.

back.jpg

I have not worked on the landing area yet, but it appears that i need to do something there to keep the rise of the first and last steps consistent.

The old stair treads are 1.5' thick wood(pine?).

And I just tested on one tread by screw 10 2' screws from under side, and it does not change much.(maybe a little bit better?) And I noticed when I step on one tread, the other treads are also squeaking....

oh boy....