Issue – USB powered GSM Modem’s Audio Out to PC’s Mic

I am trying to record audio from the Usb powered GSM Modem's Audio Out Pin using my PC. I have used a 2.5mm to 3.5mm audio jack feeding Modem's Audio to the PC Mic interface. But I am hearing the EMI noise that usually generated when you bring your mobile in a call to an unshielded speaker system.
The system works well when I attach my mobile handset to the 2.5mm end of the audio adaptor and I am able to record clear audio. The issue arises when I use the gsm modem which is powered from the same PC and feed its audio to the PC Line In or the Mic. The modem I am using is Samba 55. The last image is the adapter connected to the mobile phone, works well and i am able to record clear sound. Can any one suggest how can i remove the EMI noise?

Hi .
This simple filter may help you

thanks Ian, I am trying it in a while, will let you know about the progress in some time.

Hi .Moshin.

The filter also helps to clean up a lot of noise from the line out of a computer sound card too