I believe that is the ABS Module & what you hear is the Pump Motor Running.
Should have an OBD Code CO265 in the system -- possibly -- you should have
checked for codes already !
If you go to You Tube Video & type in (2000 GMC Sonoma ABS Module)
there you will find several Videos on how to repair the issues.
You remove the Module from the top of the the block where you see your
6 brake lines.
You open it up & follow the videos on where to resolder the 4 power & ground pins
& on the other side of the circuit board, the couple of relay pins.
Apparently a common problem with failed solder joints on many GM Vehicles
either side of yours.
You Do Not want to replace the Module due to cost & the fact it can be fixed yourself
or by a family member that can use a soldering iron & magnifying glass.
Your going to have to remove the ABS Fuse & Charge the Battery or it will run down.
You can drive without the abs pump working (in many cases)