Possible Clues:

• Jack-hammer sound
• What you may hear from drummer at a tattoo
• Knock what's said on departing into desert
• Sound of knocking on a door
• Sound made by a rapper
• Knock back door before returning thanks three times
• Sound heard in a parade
• Knock back door before returning short expression of gratitude repeatedly
• Sound of visitor's arrival cheers sailor up
• Short sharp knocks on a door