I have been searching the manual for a while and can't seem to find if it's possible to loop a sample in Rapture Pro.  I'm trying to use the white noise in it but they are not continuous loops

there is a "loop" command within the sfz format, that you could use perhaps. IRC it has layers? so instead of calling the sample, call the SFZ with the extra commands in, and in turn that calls the loop.
 
 
there is a flag for loop in certain audio types as well that support loop, only reason I know that is from doing such things for my phone ringtones.
 
this might be worth a read also.
 
http://forum.cakewalk.com/making-looping-samples-work-with-dp-rapture-m840288.aspx