[1.1.2][Phone Calls][High pitched sound]

Hi, I have a 1.1.2 which does have custom apps etc installed. My problem is that when people ring me/when I ring them they can hear a high pitched sound on there end whenever they talk. I'm not sure if this problem occurs when everyone rings me, but I know for a fact it happens with 3 phones.

Anyone have any ideas? I thought it might've been the headphones & mic while walking in the wind or something, but when I tried it without using the mic, it still happens.

Thanks :)