Possible causes:
-the lights are too intensive (can you imagine such intensity in real life? unless it's a night photo taken with long exposure ;) )
-detail in bump map (or other map? reflectivity/glossiness?) of the floor is too fine - if the details are smaller than one pixel, you might be getting such noise, the solutions would be to:
a) increase filtering blur for the bump bitmap
b) render in higher resolution
c) set internal resolution to 2 in render setup > system (but be careful with that, especially if it's a hi-res image)
-per-pass glossy reflections quality can be improved by increasing GIvsAA value - you are probably getting too much antialiasing (passes) in comparison to GI samples. You can try increasing GIvsAA to 32-64