Ford Focus noisy power steering

[Beautiful South Martin 24]

Just bought a Ford Focus 1.6 Auto 2012 (62) which has developed a high pitched noise which goes off when you put it on full lock. My local indy diagnosed new power steering pump, changed that still the same, he also replaced the power steering fluid which when he bleeds it off with the reservoir cap off seems to cure it, but as soon as cap is replaced after about 5 minutes the noise comes back. He is now saying it must the steering rack, which is going to cost an arm and a leg no doubt. Anyone had a similar issue and managed to sort it without the expense of a new rack?....Thanks