  In this work, we implement the $13^{th}$ order semi-analytical WKB method to
explore the stability of hairy black holes obtained in the framework of
Gravitational Decoupling. In particular, we perform a detailed analysis of the
frequencies of the quasi-normal modes as a function of the primary hair of the
solutions with the aim to bound their values. We explore a broad interval in a
step of 0.1 of the hair parameters. We find that except for some cases where
the method is expected to have poor accuracy, all the solutions seem to be
stable and the role played by the primary hair is twofold: to modulate the
damping factor of the perturbation and to decrease the frequency of its
oscillation.
