I'm have a 6-instrument instance of the GPO loaded up (violinKS, violinKS, violaKS, celloKS, pianoLITE, timpani) in my PTLE session, and any kind of rolling on the timpani kills the timpani sample and starts to make a digital clicking sound at about 60bpm that slowly fades to nothing. The only way to fix it is to reload the timpani samples.
The clicking sound in PT is your processor getting overloaded. You didn't state what kind of system you're running. NI's Kontakt player is not very efficient in PT on a low end system.
Make sure you're running the latest version of PT and have the most recent Kontakt player download.
Lower the polyphony wherever you can, raise the buffer. If all else fails convert tracks to audio, then freeze those aux. tracks. That'll free up some cpu resources and should help with the clicking in the Timp track.