Did you assess the deflection of the joists before beginning? Possibly reinforce those joists to be stiffer? Put down a new 3/4" subfloor? Put down cement board or a decoupling membrane on top of that? Use sanded caulk at all changes of plane between the horizontal and vertical (like your tub and any wall)?

All of that is necessary for a tile installation.

"Maybe this post will help someone else in the future."

Grout does not get used at changes of plane in tile work.

Caulk does.

Yes, thank you. It wasn't grout up against the tub. It was just a few little bits of mortar that I had to carefully look in the 1/8" gap to even see them on the floor. I didn't mortar up to the tub but obviously I wasn't as careful as I should have been. We will caulk there as well.

i'm having the same problem with a new bathroom renovation. i have an acrylic bath tub installed with the tile floor grouted right up to the bath tub side. the gap is 1/8 and i'm wondering what is the best way to remove the 60" grout line between the tub and tile. and if there is mortar up against the tub, how would that be removed?

the squeak is driving me nuts.

If you have a squeak, you have bigger problems than just grout or thinset rubbing against your tub - you have too much deflection in your floor for your tile installation.

As to removing the grout, a Dremel with a carbide grout removal bit will do the job.

Thank you all so much for enlightening us to the gap between tile and tub. As soon as my husband removed the grout, the squeak went away. It was close to a miracle that we discovered this solution!!!! And it avoided a huge problem.