02 350 7.3L ABS Hydraulic Control Unit

[dtjhtb]

Recently started hearing a loud but short buzzing/vibration coming from ABS ECU before starting (ignition "on"). The wife noticed it, so it must be something:-) No codes are being thrown, but expect one forthcoming. Anybody have an idea what might be causing the sound and should I worry? Recently replace rear rotors and pads and seems to be functional as is.

[NCHornet]

What are you using to scan the truck? You do know the FREE scans won't work on out trucks because we are not OBDII compliant due to our GVWR.