DO NOT ALWAYS think it is the batteries!
I found my problem by the destruction method.
After removing the sounder, splitting it then trying new batteries it was the same. I then ripped the piezo sounder apart and that was the problem - it was buggered! Even with power applied across it it still sounded like a whispering budgie with a sore throat!Tried a new piezo sounder from Mapkins and it worked. Problem now is that it cannot be repaired because the piezo sounder is welded in in so many places it destroys the housing getting it out.
As the batteries are such a pain to fit it might be best if the cost is saved and a working unit is aquired in the first place.
Some joker comany told me they do a specially made up battery pack for which you had to cut away the cell housing for it to fit. By the time the cost of the battery pack, the cost of the 'it is made to order' charge, the cost of the postage AND the cost of the minimum order penalty was taken into account it would have been more than a brand new sounder from the dealership!
Not to worry,
I have picked up a nearly new one for 20 notes and its perfect again.