  Interaction-induced charge orders with electronic origin occur as states of
spontaneously broken symmetry in several materials platforms. An electronic
mechanism for charge order requires an attractive component in the effective
charge vertex. We put forward such a mechanism for the formation of
unconventional charge density waves in a metal. These states result from the
condensation of particle-hole pairs with finite wave vector and non-zero
angular momentum and correspond to bond or loop current order on a lattice. The
mechanism we describe can be viewed as Kohn Luttinger analysis in the
particle-hole channel with finite transferred momentum. It incorporates
one-loop spin and pairing correctionsn, which are then used as an input for a
summation in the charge channel triggering an instability. We extend our
analysis to a spin-fluctuation approach, where the effective charge interaction
is dressed by the particle-hole ladder with exchanged momentum. We argue that
this mechanism works for weakly-interacting metals with nested Fermi surface
and a large number of fermion flavors. We apply the Kohn-Luttinger-like
approach to square- and triangular-lattice Hubbard models with SU($N_f$)
flavour symmetry and show that it leads to different types of $p$-wave charge
density waves. We also study effects beyond weak coupling at and away from Van
Hove filling in terms of a phenomenological model with additional exchange
interaction. In the vicinity of Van Hove filling, we obtain $d$-wave charge
density waves with wave vectors determined by nesting as leading instabilities.
In addition, we find another charge density wave with wave vector $K/4$ on the
triangular lattice on both sides of Van Hove filling. We demonstrate that this
$K/4$ instability can win the competition against pairing for $N_f=4$ via an
unbiased functional renormalisation group calculation.
