Humming noise and urging after water pump and serpentine belt replace at the service center

After water pump and serpentine belt (drive belt) replace at the Perodua service center - Alza develop humming noise and having the urge to move forward quite strong when pressing brake while on gear D or Reverse engaged. 

Quite an intriguing problem that still linger in my mind - what could be the problem? Anyway, below are some initial thoughts potential root causes.

• Serpentine belt (drive belt) slip - drive belt slipping could cause the urge as it skips and turn on every cycle of the rotation.
• Defective pulleys such as water pump or belt tensioner.
• Engine oil leaked on the serpentine belt to cause the belt to slip.

Already checked:

• Crankshaft pulley - looking good as the timing mark still position correctly.