Alesis ADAT-XT20 Reference Manual page 10

Setting Up: Chapter 1
should remain connected so that the shielding properties are retained,
even if there is no direct path for ground.)
Please note that not all hums and buzzes are caused by ground loops;
your cables must be of very high quality, particularly with -10 dBV se-
tups. Refer to page 9 for more information.
ADAT XT20 Reference Manual 9