problems with 146

[Newalfaman]

Hope someone can help me with the below!

1) car sometimes makes small vibrating/rumbling noise when decelerating in 3rd gear - any ideas?
2) Alarm is too sensitive - how do I turn the sensetivity down? & how on earth do I get hold of a replacemnt alarm key? so I can turn the it off(small barrel type key that fits in lock inside boot)

Aside from these points, the car is great!

cheers