Sounds like you have a very weak signal from the tower. The signal is not above the "noise floor" of the receiver. Sometimes it will just break above the noise floor and you can hear it; if propagation is good you might temporarily hear it. However you will not be able to improve the signal if it is below the noise floor. Better antenna, directional antenna, moving antenna higher will improve the signal to increase and move out of the noise floor level . Receivers have a noise floor which includes noise from the internal components ( Eg transistors, etc). It is a fixed level that cannot be changed, unless by different design circuitry. More expensive receivers with higher tolerance components will have a lower noise floor value, and allow you to receive DX signals that cheaper units cannot descern. Improving antenna performance, better cabling, and a list of other that forum members can suggest will better your chances. However in you particular case the filter will not improve your problem since the signal is below the noise floor limits.