My metal bathtub was making a cracking sound...now it has stopped. Mostly. A few weeks ago, while in the shower, I stepped forward and heard a cracking sound that made me think the tub was about to fall through the floor. It was only happening on the front half of the tub--if I stood in the back half, no sound. This went on for about two weeks, then...it stopped. Mostly. Now, I can get it to make a cracking sound only if I step directly on to the part farthest to the front and put all my weight on it. The tub is metal. The house is American Craftsman bungalow, up on pier and beam foundation. There are no visible signs of breakage--no cracks in the tub itself or around the exterior, the grout, the tile connected to its sides, etc. The tub is "installed" into the floor and wall itself (not a pedestal) and everything looks just fine. I looked under the house and I cannot see the tub, but I can see the wood underneath it (the supports? the crossbeams? the studs? whatever) and I cannot see any visible damage.
And now I don't know what to do.
Is it going to fall through the floor?
Is it just a cracked lining that has now completely cracked itself out?
Any ideas would be greatly appreciated.
Thank you!

I do not know what is happening to the tub, but it is NOT going to "fall through the floor".

if the tub is not seperating from the tile around it, it is not falling thru anything. the tub is not connected in any way to the walls around it.
americast tubs are made of steel with a liner attached to the bottom and sides. one possibility is that you have one of those and the steel and the liner are seperating ??

Is the tub made by American Standard?