There are many parameters to an analog PSTN line, dahdi does it’s best to use sane and common parameters but sometimes your line might be out of “spec” on battery voltage, line loop current and a whole bunch of other parameters, from the code
module_param(debug, int, 0600);
module_param(loopcurrent, int, 0600);
module_param(reversepolarity, int, 0600);
module_param(robust, int, 0600);
module_param(opermode, charp, 0600);
module_param(timingonly, int, 0600);
module_param(lowpower, int, 0600);
module_param(boostringer, int, 0600);
module_param(fastringer, int, 0600);
module_param(fxshonormode, int, 0600);
module_param(battdebounce, uint, 0600);
module_param(battalarm, uint, 0600);
module_param(battthresh, uint, 0600);
module_param(ringdebounce, int, 0600);
module_param(fwringdetect, int, 0600);
module_param(alawoverride, int, 0600);
module_param(fastpickup, int, 0600);
module_param(fxotxgain, int, 0600);
module_param(fxorxgain, int, 0600);
module_param(fxstxgain, int, 0600);
module_param(fxsrxgain, int, 0600);
all of which can be overridden as you load your modules, but I suggest you need to call “repair” and have them check that your trunks are properly provisioned at your premise, and there is no problem with the “local loop” compared with your other non-problematic trunks.