  In this work we consider a class of interacting vacuum corresponding to a
generalised Chaplygin gas (gCg) cosmology. In particular we analyse two
different scenarios at perturbation level for the same background interaction
characterised by the parameter $\alpha$: (i) matter that follows geodesics,
corresponding to homogeneous vacuum, and (ii) a covariant ansatz for vacuum
density perturbations. In the latter case, we show that the vacuum
perturbations are very tiny as compared to matter perturbations on sub-horizon
scales. In spite of that, depending on the value of the Chaplygin gas parameter
$\alpha$, vacuum perturbations suppress or enhance the matter growth rate as
compared to the case (i). We use Cosmic Microwave Background (CMB), type Ia
supernovae (SNe) and Redshift Space Distortion (RSD) measurements to test the
observational viability of the model. We found that the mean value of our joint
analysis clearly favours a positive interaction, i.e., an energy flux from dark
matter to dark energy, with $\alpha \approx 0.143$ in both cases, while the
cosmological standard model, recovered for $\alpha$=0, is ruled out by
3$\sigma$ confidence level. Noteworthy, the positive value of interaction can
alleviate both the $H_0$ and $S_8$ tension for the dataset considered here.

Cosmology and Nongalactic Astrophysics