Ok guys, so here it is! I finally got the time to take out all the sidings and floorings and all those plastic covers that beautify the rear portion of the X5 E53. Drove it around for a week and discovered all those noises and ofcourse the cause of the TOK TOK I was complaining about!

You wouldn't believe where the TOK TOK was coming from! After all the frustrations, sleepless nights, disassembly hand wounds and enormous time consumed to find this TOK TOK knocking sound....I finally found it!

It was ALL the 3 REAR LATCHES that are not aligned and therefore created the unsynchronized sporadic untraceable knocking sounds because they were coming from 3 different sources. The latches locked too loosely (probably due to its age and consistent banging through the years) hence the mis-alignment of all my latches.

Solution: I haven't decided on taking down the latches and re-adjusting them so that they lock and fit tightly... So, I just simply TAPED the LATCHES using a rubberized electrical tape. Now the knocking TOK TOK sounds are gone completely after I installed the TAPE. I'm not sure until when the TAPE will hold but I'm seeing some tears already from the center latch after only a few days drive. If and when the metal gets exposed, I will just put another layer of this inexpensive electrical tape!

Lesson learned - Most of the time, the reason for a certain situation is the obvious reason and therefore the solution to this simple situation will ofcourse be the simplest solution! Lets avoid complicating matters! hahaha! Hope this helps! Cheers!