  In this study, we examine the long term torque noise fluctuations of
persistent Xray binaries Her X-1, Vela X-1, GX 301-2, CEN X-3, 4U 1538-53, OAO
1657-415 and 4U 1626-67 using the historical pulse frequency measurements
provided by CGRO/BATSE and Fermi/GBM. We find that known disk-fed sources
exhibit $1/\omega^{2}$ red noise component in their power density spectra which
is saturated over long timescales. On the other hand, wind-fed sources form a
clear white noise component and the wind-fed sources with occasional transient
disk formation imprint $1/\omega$ type flicker noise. We discuss their
long-term timing noise properties based on the models to describe the power
density spectrum of pulse frequency derivative fluctuations in terms of
monochromatic and colored noise processes. Furthermore, we investigate the
relation between measured timing noise strengths and other independently
measured physical parameters. Despite the low number of sample sources, we
suggest that noise strengths of these sources are correlated with their
luminosities and uncorrelated with their magnetic fields strengths, implying
that the dominant noise generating mechanism is accretion
