Went to internet, found out what to test (PRAM, SMART, disk utility verify disc etc, )did all that. Made Genius appointment, got confirmation from them, then called Aftersales, whilst in the Apple store. Said truthfully it was my main machine, I needed it for thesis work, that it'd taken x days to arrive, and since within 14 days, looks like hard drive problem that could be failure imminent, that I wanted a replacement sent out, and that i'll return the old one when the new one comes thank you very much. Had to escalate tone and firmness a little, but got the deal - YMMV
Getting to right dept helps (having been transferred to the Spanish dept for 15 minutes instead of aftersales/tech support/refunds - bought through HE so had option of going through that dept too).
Fingers crossed, the replacement isn't making a squeak. The bottoms flexible as last one, but the vibration is much less (still there with the resonant buzz feeling if you move fingers round the left hand side of the trackpad, but much better than MBP i'm returning.
If you can, get a Genius appointment and call from the Apple store - helps credibility as info will be on your account, and you'll get Apple help either way.