I had a similar dance with Apple tech staff. I took in a 27" iMac which had a faulty video card fan which made a horrible high pitched whine at low brightness settings.

First visit they couldn't hear it (in loud store environment..), I was sent home. Second visit they agreed to take it in for testing - returned with a chipped display, scratched glass and a report that the problem didn't exist.

Finally gave up with them and called Apple USA direct (from UK), complained to anyone who would listen. Was advised to take into a 3rd party repair supplier to confirm the problem existed. I went in with an audio spectrometer to visualise the problem, had a new iMac shipped the next day.

It's hard to accept that they're no longer the specialist hardware supplier who treats every customer exceptionally well. Now we're just being farmed like any customer.

Going hackintosh/linux for all future machines.