Clicking sound when i walk. Need advice

[Spud]

did you allow a 3mm gap between the sheets of ply when they were installed how did you adhere the ditra matting to the ply? did you flat the ditra matting off with rapid set then allow this to dry then tile ?or did you tile straght on to the ditra matting with rapid set? what size notched trowel did you use ?

 

[CJ]

Are you 100% sure the builders had ALL the ply joints right on the joists?
Something is moving..........either A joist or a ply join.

Are the hairline cracks in a straight-ish line?

 

[grumpygrouter]

Sorry meant to say "i would have a much greater chance of the tiles not cracking and using the ditra than putting the tile down straight onto the ply".

Ditra will only help with lateral movement, it will not help at all with deflection. If the ditra deflects even a couple of mm I suspect your tiles will crack.