Crown molding is trim that goes along the ceiling. Are you talking about baseboards?

A photo of the problem area would be helpful.

yes i apologize the base boards is what i meant. I'll take pictures next time i go there but here's a drawing of what i'm talking about from a side angle

There may be dips in the floor itself and that may be why the bottom of the baseboard does not touch the carpet in some places.

Baseboard in rooms where carpet is scheduled is usually installed first and then the carpet is fit up to that...at least that is how it is usually done in my neck of the woods.

Also, the location of the tack strip which can easily not be in line with your baseboard can cause gaps. Low pile carpet can exaggerate this condition. A baseboard which isn't straight can cause the problem (they do warp).