Here is why they care..
If...you make money on it....they will want a piece of it...
They could always claim that your tracks are worthless without the sound bites.
This is a legal issue better answered by others though...perhaps an entertainment attorney.
I am not sure but, I believe that you would have to petition the various owners of the copyright protected sound bites for a liscensing agreement.
That is if they all come from say a film or video which is copyright protected...
If it is from an interview, say on the news....you might be in a better position...they are more than likely copyright protected as well though.
I am unsure but, believe me....it is better to know now than later.
So, hopefully someone else will have a better answer than this.
Good luck,
Joe