Agree with hokie66....a hollow sound means poor bond. If the bond is poor, even over a crack mitigation membrane, you will hear some level of sound change between good and bad.
Drying shrinkage occurs over an indefinite period. As hokie66 notes, changes in interior environment conditions will change the conditions of shrinkage. Adding a crack mitigation membrane usually slows shrinkage because it keeps the slab from drying at a faster rate. Shrinkage still occurs, just at a slower rate. The crack mitigation membrane moderates the horizontal shear between the slab and the thinset. If you use a flexible tile adhesive, you won't need a mitigation membrane. Flexible tile adhesives are not usually used for floor slabs in the US, but are commonly used in other areas (don't you use flexible adhesives in your area hokie66?).
As for crack mitigation membranes to use, if it is only for crack mitigation you can use a roll-on product like RedGuard or Mapei. If you want to mitigate both sound and cracking, a sheet membrane like Profiles is used.