I have the very same problem with a fresh Win7 64-Bit (Scratch Pro, Kontrol X1, Audio 8 DJ). In the beginning everything worked as it should but after a time it begun to crackle and adjusting the buffer sizes didn't helped. Even with 64ms it crackles. OMG. I noticed that the CPUmeter is bouncing all the time unregularely, although nothing is running in the background.
So today I took an old HDD and installed WinXP 32-Bit on it and Traktor runs fine, even with 1,5ms buffer and the CPUmeter doesn`t bounce anymore.
I don't know where the problem is. You said you have Win7 32-Bit so I guess it has nothing to do with the 32/64Bit-architecture, but with Win7 itself?
Maybe there is something to fix in Traktor to make it more compatible to Win7, because I noticed we are not alone with this problem.
My system specs are:
AMD Athlon 64 X2 DualCore 5000+ (2,7Ghz)
Nvidia GeForce 9500GT
2 Gig RAM
so I think my system should be good enough