Tape, blob of silicone, blue tak or the crunch method are all things I have used.
Last was an alarm control panel that was beeping due to it failing it's self testing, and a 2 week delay for a new one. Still in there, just loose and rattling around.
BTW why the bleeping kettle? Gas powered one has a whistle, and the electric simply switches itself off anyway. You know the power consumption of that kettle is doubles, simply from the always on power of the electronics. Just like the clock display in a microwave uses more energy over the life of the microwave simply from being on 24/7/365 at 10W or so while the duty cycle of the actual magnetron is around 5 minutes a day.