Pre-ringing occurs when a linear-phase filter's impulse response extends symmetrically in both directions from the main peak. The energy before the peak is pre-ringing — an unnatural artifact (real-world sounds cannot ring before they happen). It is most audible with: very steep filters, low-frequency correction (where filter lengths are longest), and percussive material with sharp transients.
Mixed-phase and minimum-phase filters avoid pre-ringing (their impulse response extends only forward in time, like real acoustics) at the cost of phase shift. This is why many room correction systems offer multiple filter modes — linear-phase for maximum accuracy, mixed/minimum-phase for natural transient response.