Guitar riff:

D harp (3rd position):

-3//    -3//   -3//    -3    4   4   4   -3

A harp (2nd position):

-1   -1    -1    2   -2//    -2//    -2//    2

E harp (1st position):

-2   -2    -2    -3//   -3/   -3/   -3/    -3//