I tiled our bathroom floor that is a linoleum floor glued to a concrete slab floor. It looks great but a few days after I was finished one tile had a gritty sound to it when walking on it. I took it out and discovered that the adhesive was still wet after 5 days! I put in a new tile and regrouted. Now there is another tile a week and a half later making that same sound. Like a crunching sound coming from under the tile. The grout is a little cracked around it but not bad. I cleaned the floor very well before tiling. I vacuumed as well. What could be making this happen and now I'm worried that all of the tiles will eventually come loose. Is that probably an isolated incident? What should I do or look for? I read on the Internet that you can tile over a linoleum floor so I thought I was ok to do it. Was I wrong? I also tiled our upstairs bathroom a year ago but it was a wood subfloor so I put down concrete backerboard first. It seems to be in great shape.