  We study the rapid X-ray time variability in all public data available from
the \textit{Rossi X-ray Timing Explorer's} Proportional Counter Array on the
atoll source 4U 1820--30 in the low-luminosity island state. A total of
$\sim46$ ks of data were used. We compare the frequencies of the variability
components of 4U 1820--30 with those in other atolls sources. These frequencies
were previously found to follow a universal scheme of correlations. We find
that 4U 1820--30 shows correlations that are shifted by factors of
$1.13\pm0.01$ and $1.21\pm0.02$ with respect to those in other atoll sources.
These shifts are similar to, but smaller than the shift factor $\sim1.45$
previously reported for some accreting millisecond pulsars. Therefore, 4U
1820--30 is the first atoll source which shows no significant pulsations but
has a significant shift in the frequency correlations compared with other 3
non-pulsating atoll sources.
