Im having some problems with my VZ Acclaim

1 - when you lock the car the horn sounds - cheacked the car and realised the rear passenger door isnt locking - is likely that the actuator needs replacing?
If so is this very expensive as the cars not under warranty

2 - rear passenger window switch lets the window go down but not up.
The window goes up and down fine if using the front switches.
Would it be as simple as buying a new switch?

3 - there was a Nokia bluetooth car kit installed in the car when i bought it.
It originally worked fine but lately has started making loud buzzing sounds through the speakers when taking or making a call.
The person on the other end doesnt hear any problems its just in the car.
Any suggestions on what wrong with it?