In the Sub 37 MIDI menu, try changing the MIDI In Channel setting. If it is set to All, trying changing it to 1. If that still responds to DrumBrute notes try changing it to 2. If it is already set to 1, try changing it to 2.
Clock sync should work even if the channels don't match, because clock messages are not channel specific, but note messages are.
The Sub 37 PDF manual is available here:
Page 35 has the MIDI menu instructions.
Press the MIDI button to open the MIDI MENU. This menu contains parameters associated with the
sending and receiving of MIDI signals. When the MIDI button is illuminated the top right of the LED
display will indicate which page you are on, followed by a decimal point, and then which parameter
line you currently have selected. Use the [Up Arrow] [Down arrow] buttons to choose a parameter for editing, and the
FINE TUNE knob to scroll through a selected parameter’s available options.
NOTE: You can also use the CURSOR button to select a parameter and the [Up Arrow] [Down arrow] buttons to step
through the selected parameter’s available options. To exit a parameter, simply press CURSOR again.
If more than one page of parameters exists, continuing to press the [Down arrow] button will take you
through the additional parameters and pages. If the MENU WRAP parameter (GLOBAL MENU) is
OFF, the [Down arrow] button will stop working at the last parameter of the last page.