Just had a new alternator fitted and on return of the car, when reverse gear is engaged, it sounds continuously. Can this be attributed to any reconnection of the alternator or might there be an alternative explanation.

 

What "sounds continuously".? Volvos did not come with a reverse warning or beeping system.

 

When put int reverse gear, all is silent till there is an object in the way, then a bleeper sounds in the cab which increases in number of bleeps till you get too close then there is a continous bleep. well when I put the car iinto reverse, the bleep is immediately conyinous as if there is an obstruction there. This has happened when the car was returned after the replacement of an alternator. Is it coincident or connected ?

 

You have parking sensors, - If you look at your rear bumper there are 4 round 5/8 inch sensors. When working properly - if you get a few feet away in reverse, you get a beep, and as you get closer to something the beep gets faster then solid.

If your parking sensors are causing a beep whenever you are in reverse - those sensors are confused or damaged.
Is there something else happening? Is it beeping at the wrong time when nothing is there?

An alternator replacement would not create that problem. Damage to your rear bumper might!

 

There is also a button beneath the radio controls to turn them off, if that is what you are hearing.