  We report voltage-clamp measurements through single conical nanopore obtained
by chemical etching of a single ion-track in polyimide film. Special attention
is paid on the pink noise of the ionic current (i.e. $1/f$ noise) measured with
different filling liquids. The relative pink noise amplitude is almost
independent of concentration and pH for KCl solutions, but varies strongly
using ionic liquids. In particular we show that depending on the ionic liquid,
the transport of charge carriers is strongly facilitated (low noise and higher
conductivity than in the bulk) or jammed. These results show that the origin of
the pink noise can be ascribed neither to fluctuations of the pore geometry nor
to the pore wall charges but rather to a cooperative effect on ions motion.
