I have a full Aguilar DB751 rig, Markbass Classic 300 rig and a new UL901 rig.
The UL901 has a low level hiss through the cabinets regardless of the gain/master level, I measured it at about 29dBa at 1m.
The UL901's hiss is much lower level than the DB751's fans (ugh!) or the Classic 300's...