Blackface nosie

[Dr Shock]

Are the 16 bit AD converters known to be noisy? I am using my blackface ADAT's as a way to receive audio out of my PC card ( Hammerfall 9652 ) through lightpipe and then from the ADAT into my Mackie 8 bus with the ELCO +4 balanced signal. I am hearing a lot of line noise and wondering if these ADAT converters are known to be noisy, or if there is reason to suspect the noise is coming from somewhere else. When I monitor signal just throught the Mackie, the signal is clean

thanks