Could be related to the acceleration height also even you fly the sid with insane precision. depends on the noise characteristics of the plane also what you get away with , as i remember the spiderweb of noise monitoring points in some places are set for a max decibel value. 2 minutes in could be difference between a nadp 1 or 2. Not sure which one they want you to do in Frankfurt. Think they should be able to send a printout with their complaint so you can check the track and see your track in relation to the sid.