I had 2 tapping noises from the rear -
1 was suprisingly loud for a small item - one of the rear number plate lights was loose. Tightened the screws but it did not stop and found a sealing gasket was missing.
The other was a wire loose (leading to my rear parking sensors) behind the R/H side boot trim. Trim is a bit of a sod to get off, so I got the rear free enough to jam some foam in, on the wire. Waiting for warmer weather to do a proper job.
Hope these might help.