The buildup of the modes of a He&sngbnd;Ne laser in the presence of other strongly oscillating modes was analyzed. Owing to the gain interaction the buildup time was found to be about one order of magnitude greater than for freely growing modes and to be greatly dependent on the position of the modes under the Doppler curve. The active bandwidth for the low‐frequency noise due to the presence of combination tones near the modes was derived from these measurements.