Bose QC20i earbud noise when noise cancellation active

I got the right earbud open (the original glue heated and the bud opened up). I was gluing this back but then when the noise cancellation is turned on, a whistle-like nose happens in this bud only, making them impossible to use. What did I do wrong? Anybody knowing how the noise cancellation is done? It seems what doing the gluing process I have done something wrong…