The present invention relates to a method and a communication network node for enabling auto-tuning of preamble sequences used during random access procedures when user equipments (18) are accessing a communication network system comprising radio base stations (15) each serving at least one cell (19) and with which said user equipments (18) are communicating on uplink (13) and downlink (12) channels. An initial set of RACH preamble sequences in one cell of a radio base station (15) and statistics on RACH usage and information on identified RACH preamble sequences potentially conflicting between neighbors of said radio base station (15) is collected. The collected statistics is used for optimizing said set of RACH preamble sequences, whereby the initial set of RACH preamble sequences is replaced with the optimized set of RACH preamble sequences.