DAT recording and SPDIF

I have a Live! CT4620
I've a problem about SPDIF connection with my DAT.

Just few days ago I transfer without problem tracks recorded with my
DAT using the SPDIF connection (coax cable) with fine result.

I have an issue during a recording session: a very loud sound appear
during the recording (I can heard it from the loudspeakers and can see
it from the level meter in the recording program).
The sound was related with the soundcard, because it stay without
signal at the imput.

Now the situation is:

1- I can listening DAT source with the PC ( recorder tracks or using
tape monitor) as a correct sound.

2- If i record from DAT source trought SPDIF in or analogue in (Line
in) the sound is distorted by a "frying rumor" that shadow the sound.

If I change the recording source I don't solved the problem.

Is something related with hardware issue in the soundcard ?

Any suggestion ?