To say or speak in a rapid or mechanical manner. (Merriam -Webster)
Continuous and sometimes funny speech or talk, especially used by someone trying to sell things or by an entertainer. (Cambridge Dictionary)
If something patters on a surface, it hits it quickly several times, making quiet, tapping sounds. (Collins Dictionary)
A patter is a series of quick, quiet, tapping sounds. (Collins Dictionary)
Make a repeated light tapping sound. (Oxford Dictionaries)
Patter sound effects.