  We have analyzed ~600 ks of Rossi X-ray Timing Explorer data of the neutron
star low-mass X-ray binary and Z source GX 17+2. A study was performed of the
properties of the noise components and quasi-periodic oscillations (QPOs) as a
function of the spectral properties, with the main goal to study the relation
between the frequencies of the horizontal branch and upper kHz QPOs. It was
found that when the upper kHz QPO frequency is below 1030 Hz these frequencies
correlate, whereas above 1030 Hz they anti-correlate. GX 17+2 is the first
source in which this is observed. We also found that the frequency difference
of the high frequency QPOs was not constant and that the quality factors (Q
values) of the HBO, its second harmonic, and the kHz QPOs are similar, and vary
almost hand in hand by a factor of more than three. Observations of the normal
branch oscillations during two type I X-ray bursts showed that their absolute
amplitude decreased as the flux from the neutron star became stronger. We
discuss these and other findings in terms of models that have been proposed for
these phenomena. We also compare the behavior of GX 17+2 and other Z sources
with that of black hole sources and consider the possibility that the mass
accretion rate might not be driving force behind all spectral and variability
changes.
