Interlocutor hears loud hum after change of dock connector

Hi, I had to change the dock connector due to a malfunction of the headphone jack. After the repair everything worked perfectly first. However, after a couple of calls my dialogue partners started complaining about a loud hum - similar to a noise you hear if you have a call near to a loudspeaker (like a network hum). So I assume that there is something wrong with the antenna - but I do not understand why it worked directly after the repair. Thanks for your support.