[Adso]

This from the Manual ... Could be a ABS System Check???

computer. The computer has a built-in diagnostic
feature that tests the system each time you start
the engine and move the vehicle at a low speed in
forward or reverse. When the self-test occurs,
you may hear a "clunk" noise and/or feel a pulsation
in the brake pedal. This is normal and is not
an indication of any malfunction.

Hope that helps