i think mine is slipping - i hear 'squeally' noises from
the back of the car which i believe is this, but i replaced it with another one (a few months
ago) the problem got better but was never perfect. have i just got another duff driveshaft or is
something else the problem?

Try to send a sound file so we can hear your problem!

it is quite common 340 problem. but
usually the front end of the shaft breaks. can you install it backwards and listen to the
geography of the noise? or maybe find the trouble-making-point visually?