QC30 Rubber cover issue is caused by the case
There has been many posts regarding this issue. Unfortunately once you are here it happened to you too.
I bought my QC30's about 2 years ago. The rubber cover is falling off. And due to this issue the sound is getting worse. As my QC30's are still less than 2 years old I could have them replaced. They are still under EU warranty. I don't want another model as the QC30's are just what I need. And I have the cure for this rubber cover issue:
For those of you who had them replaced or those who are in the process to have them replaced: well, just DON'T USE the Carrying case anymore. Because when you take the QC 30's out of their Carrying case you just force the rubber to fall off after just a few operations like this. And that is because the headphones are a little bit bigger than the Carrying case and you need to force them a bit to get inside. And the part that is forced to go inside is exactly the part of the headphones that will eventually peal off - the rubber cover.
Or if you really need a carrying case for them, just don't use the original one. Improvise. Place your QC 30's in a bigger case.
Good luck with that!