  Muon Spin Rotation/Relaxation ({\mu}SR) is a powerful probe to study
diffusion of hydrogen-like particles. One of the most common model to analyze
{\mu}SR signals from materials where diffusion occurs, is by using functions
derived from the stochastic theory of Kubo and Toyabe along with the strong
collision model. Unfortunately the current formalism can not be used to analyze
data from systems where not only muons diffuse, but also the magnetic moments
of the material are dynamic. In this article we introduce a new model which
accounts for both dynamical effects, and use this model to analyze {\mu}SR
signals from Dy0.4Y1.6Ti2O7.
