  The ubiquitous presence of $1/f$ flux noise was a significant barrier to
long-coherence in superconducting qubits until the development of qubits that
could operate in static, flux noise insensitive configurations commonly
referred to as `sweet-spots'. Several proposals for entangling gates in
superconducting qubits tune the flux bias away from these spots, thus
reintroducing the dephasing problem to varying degrees. Here we revisit one
such proposal, where interactions are parametrically activated by rapidly
modulating the flux bias of the qubits around these sweet-spots, and study the
effect of modulation on the sensitivity to flux noise. We explicitly calculate
how dephasing rates depend on different components of the flux-noise spectrum,
and show that, while these parametric gates are insensitive to $1/f$ flux
noise, dephasing rates are increased under modulation, and dominated by white
noise. Remarkably, we find that simple filtering of the flux control signal
allows for entangling gates to operate in a novel sweet-spot for dephasing
under flux modulation. This sweet spot, which we dub the AC sweet spot, is
insensitive to $1/f$ flux noise, and much less sensitive to white noise in the
control electronics, allowing for interactions of quality that is limited only
by higher order effects and other sources of noise.
