Hi dahjah,
I was looking for something like this recently after I moved from an old system (that had the excellent Sound Forge Noise Reduction plugin) to a new one that didn't.
Halfway down the attached thread, there is a suggestion from
musicroom that I should try a free plug-in called
reaFir.http://forum.cakewalk.com/Upgrading-from-SONAR-3-to-X3-a-Sound-Forgey-question-m2977472.aspx I've installed it and it does the job perfectly.
I can simply sample an isolated bit of hiss and then select to have it removed from the remainder of the clip.
Some instructions are here:
http://reaperblog.net/2012/05/video-removing-noise-with-reafir/ It works slightly differently as an in-line plug-in but it wasn't difficult to work out once I'd got going...
Good luck if you try it,
For the record, I've submitted a request to Cakewalk that this plug-in (or something similar) is an in-built or a bundled tool for future releases of SONAR (you never know).
Frink