The regular and profinite representations of residually finite groups

Let $G$ be a residually finite group. To any decreasing sequence $\mathcal S = (H_n)_n$ of finite index subgroups of $G$ is associated a unitary representation $\rho_{\mathcal S}$ of $G$ in the Hilbert space $\bigoplus_{n=0}^{+\infty} \ell^2 (G/H_n)$. This paper investigates the following question: when does the representation $\rho_{\mathcal S}$ weakly contain the regular representation $\lambda$ of $G$?