I found out that - as crazy as it may sound - in my case it had something to do with the battery brand I used.
I normally use Duracells, but always found them a bit hard to insert into the slot (it was really hard to close the lid with the battery inserted), but never had any issues until recently I bought a new pack.
Just for the sake of it I used a battery from a different brand - Varta in that case - and not only do these fit better: Noise cancellation works fine again! No more interruptions, problem solved!
Best regards, Ralph