  We have investigated the spectral and timing variability of four accreting
X-ray pulsars with Be-type companions during major X-ray outbursts. Different
spectral states were defined according to the value of the X-ray colours and
flux. Transient Be/X-ray binaries exhibit two branches in their colour-colour
and colour-intensity diagrams: the horizontal branch corresponds to a
low-intensity state and shows the larger fractional rms, similar to the the
island state in atolls and horizontal branch in Z sources; the diagonal branch
corresponds to a high-intensity state, in which the source spends about 75% of
the total duration of the outburst. Despite the complexity of the power spectra
due to the peaks of the pulse period and its harmonics, the aperiodic
variability of Be/X-ray binaries can be described with a relatively low number
of Lorentzian components. Some of these components can be associated with the
same type of noise as that seen in low-mass X-ray binaries, although the
characteristic frequencies are about one order of magnitude lower. The pattern
traced by V 0332+53 results in a Z shaped track, similar to the low-mass Z
sources, without the flaring branch. In contrast, the horizontal branch in 4U
0115+63, KS 1947+300 and EXO 2030+375 corresponds to a low/soft state, not seen
in other types of X-ray binaries. The noise at very low frequencies follows a
power law in V 0332+53 (like in LMXB Z) and it is flat-topped in 4U 0115+63, KS
1947+300 and EXO 2030+375 (like in LMXB atoll). V 0332+53 shows a noise
component coupled with the periodic variability that it is not seen in any of
the other three sources.
