4 + 1

Four Songs About Knocking and One Bonus

1.  Keep A-Knockin' But You Can't Come In / Little Richard (link)
2. Knock Three Times / Tony Orlando (link)
   
3. I Hear You Knockin' (But You Can't Come In) / Fats Domino (link)/Dave Edmund (link)
4. Knockin' On Heaven's Door / Bob Dylan (link)
5. Dave's Not Here / Cheech & Chong (link)