A commom audio transfer question in TDM16 format

Hi,

I always meet with difficulty in several different projects. When I use TDM16 format to receive datas using ADAU1452, I can get all the 16 channels audio datas and it sounds like good. 

What confused me is that sometimes for example, I copy the same datas to all 16 channels in Tx device and then send out. After I received in 1452, the datas are not the same, usually some channels sound like in a low voice than the others. I mean that the volume of some channels are lower but it's still the correct audio without any noise or click.

Please give me some issues about this situation.