BOM sound newly cast basement floor

[oscarwww]

Poured a basement floor yesterday, with reinforcement, cellplast, and isodrän underneath, it sounds a bit hollow under the sections where there is cellplast. The other sections where I've cast with only gravel underneath are very solid.

Is this a problem? Will it become solid after curing for 1-2 months?
About 7-10cm concrete.

 

[Simmeman]

The same sound on my basement floor, cast a month ago.

 

[oscarwww]

Same sound on my basement floor, poured a month ago.

Do you expect it to decrease with self-leveling compound and tiles?

 

[Simmeman]

Haven't really reflected over it. Find it hard to believe that it disappears just because you use self-leveling compound and lay tiles on top.

Also notice a difference where there is isodrän or gravel underneath.