Popping noise from earphone?

Hello.I bought my new iPhone 7 today ,updated to 10.0.2 and noticed something.On the first call after I wake up my phone,the earphone will make a popping noise once and then silence again.I am thinking of this like a turn-on-earphone kind of sound.It will not happen again,until I put my phone to sleep and wake it up again.I tried 3G,2G,4G,noise cancellation on/off to no avail and it will not happen with any other earphone use but a call.Anyone noticed this? Should I worry? Thanks in regard.