Hi guys. The dust cover was my exact problem. Damn thing driving me crazy.
On the right hand side the boot on the axle and the dust cover can turn independently. Not so on the left hand side.
The dust cover seems to be able to catch sometimes hence boot and dust cover are moving against eachother and making that awful noise.
I've fixed it for now with silicon spray. But I think a better solution is to glue the dust cover to the boot and add grease between dust cover and rear diff.
See image here:
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