Abstract: Localized paramagnetic electrons are believed to be the cause of magnetic flux noise that plagues superconducting qubits; however, how such interacting spins generate frequency dependent noise of the 1/f form is not well understood due to the complexity of the full quantum mechanical treatment of interacting spin system. In this talk I will describe a dynamical real space renormalization group (RG) procedure that allows to calculate directly various dynamical quantities in a strongly disordered Heisenberg spin systems. Using this approach we generally find the dynamics that correspond to (anomalous) spin subdiffusion, with a powerlaw low-frequency magnetic noise, which appears to be consistent with what is observed in superconducting circuits.