Is this the contractor's problem, or mine?

I recently had my entire bathroom redone - the house was built in 1930, and the bathroom was original. The only real problem was that the floor under the toilet was sinking - but I decided to have the whole thing updated, and it is now gorgeous. Except for the floor squeak. Squeak, squeak, squeak goes the floor,... show more I recently had my entire bathroom redone - the house was built in 1930, and the bathroom was original. The only real problem was that the floor under the toilet was sinking - but I decided to have the whole thing updated, and it is now gorgeous. Except for the floor squeak. Squeak, squeak, squeak goes the floor, and never did it do that before. All of the grout at the wall has separated from the floor tile. In one place, there is a 1/4" gap. The contractor had gutted the entire room, and replaced some floor boards before laying 12x12 ceramic tile. He now says that he will have to rip up part or most of the floor to fix the squeak, and he *might* have to charge me for this. I don't agree.

The house is on a crawl space, and there is plenty of room to work underneath. The room now squeaks even when the kids are upstairs directly above the bath.

Question #1 Shouldn't he fix this without charge? He did say that if any problems occurred with the work, he would fix them, at no charge. Hmm.

#2 Can it be done without tearing anything up?
Update: LOL Bill! You think Sam Bernstein can help??
Update 2: In my haste yesterday, I left out the fact that the contractor did tear it right down to the 2x10 joists, and either replaced or sistered the bad ones. On top of that went the plywood, and another board to cement the tiles to. He insists that the floor was sinking because of a bad wax ring and leakage, not... show more In my haste yesterday, I left out the fact that the contractor did tear it right down to the 2x10 joists, and either replaced or sistered the bad ones. On top of that went the plywood, and another board to cement the tiles to. He insists that the floor was sinking because of a bad wax ring and leakage, not structural damage.

Thank you all for the great advice. I definitely have more to go on now. If there is anything else you can think of... I really appreciate it!
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