Aluminum shows vigorous fluctuations in current and potential in chloride containing media close to its pitting potential. To determine the source of this noise, we used aqueous solutions, gels with a pH indicator, and currents between interconnected electrodes, to locate pits and study currents generated at freely corroding potentials. We demonstrated that there is a transition in the characteristics of the noise. Transitions occur when pits continue to remain active, and also when more than one active pit is present because of the electrochemical communication that takes place between them. The major source of current and potential transients with aluminum is due to the growth process in active pits, rather than metastable pitting at the passive surface. (C) 2002 The Electrochemical Society.