Digi 002 error inputs

[jimijo]

Hello everyone, I'll tell you if you can help me ...
I have a Digi 002 rack connected to a MacPro 2.1 with Mavericks and Logic X, the card to reproduce the tracks has no problem but when I connect for example a guitar, after a while (it can be about 3-4 minutes) the sound, only the on the guitar, it starts to sizzle and only stops when in the Avid 003 Family application where it says "Clock Source" I change the value to any other option but it sizzles again when another 3-4 minutes pass.
The truth is that it is something strange ....... I thought it could be the cable, I have already asked for one, when I get home I try it, but in the meantime, let's see if you can tell me what it could be, I hope it is not internal fault of the inputs.

Greetings and thanks.