Security of GSM 900 MHz

[leon2016]

Greetings, I just bought my Alcatel Pop C3 and while working in my PC listening music with my earphones (and having my smartphone with me), I hear some feedback like an incoming call in the cell phone. I checked and nothing is going on with the smartphone (none incoming message, none incoming call, nothing at all). It crossed my mind that someone might be trying to hack my phone, but I don't think so...Where I live we use GSM 900 MHz; my question is: is there any chance that there be any interference on the band which may be something normal, like noise in the bandwidth? or have I been hacked ?
Thankx in advance