HELP! AUX?

[Giveuinsight]

I just bought a Mytouch 4G, I plug my phone into my AUX so that I can hear my phone calls and music over my speakers, but when I get a call and I answer it, I can hear them through the speakers, but they cannot head me unless I unplug the phone from the AUX. My last mytouch worked fine doing this, any ideas?