Used car problems

[2ky]

I purchased a 2008 Seat Ibiza sport just over a month ago. The following day I noticed the air conditioning was noisy so I arranged to take the car back to the franchised (not Seat) dealer, they had a look and came back to tell me "ah we've had a polo in with the same engine and it sounds the same" I disagreed with this and the aftersales manager suggested that I take it to a Seat dealer at there expense to see if there is a fault. I did this and Seat stated the compressor and expansion valve were at fault (£1500 to replace) after a long winded claim via the after sales warranty the car was booked (at the garage I purchased the car from) to have the parts replaced. Just before going into have the warranty work done I noticed a whine coming from the gearbox and mentioned this before the car went in so they could have a look.
I got a call to say the air con was fixed and I asked about the whine and again was told "We've had another one in and its making the same sound". I completely disagree and in a huff the aftersales manager states he thinks its normal but if I want he will get an engineer out from the warranty company to have look and see what he thinks (but he doesn't want to waste every ones time and thinks the warranty company will refuse it). I'm obviously not happy with all this but I'm giving him the chance to see what the warranty company say.
The noise is definatley not normal and has got a lot louder over the last fortnight. If the engineer does not identify fault does anyone know where I go from there? I was thinking of maybe getting some sort of report from the AA or RAC? or arrange for the car to go back to Seat again ,if no fault is identified I pay for Seats time,if a fault is identified by Seat the original dealer pays?
Am I doing the right thing?