After maybe a half hour of not playing anything thru Bidule it either crackles real bad or no sound at all.
for the crackling:
This looks like either everything that was loaded into RAM by Kontakt has been paged to disk and is being brought back
(how much RAM do you have? what is the amount of loaded samples in memory?)
A way to test that theory would be to either reload the samples in Kontakt or load a new instrument(s) and
see if the problem goes away the same as in relaunching Bidule.
Does you computer sleeps during that half hour of no activity? If yes, that means that the USB
connection to the Fast Track is dropped.