Making knuckle cracking noises after repair, Apple Store said it's "normal"

Question

I sent my MacBook Air mid 2011, the first time, to an Apple Store because it failed Verify Disk and was unable to re-install OS X (Repair No.: R88048332). When I got it back and found strange knuckle cracking noises whenever I held it and moved around.  I further found a few screws on the lower case were not tightened. And with a little pressure with my thumb and pointer finger, I could see the lower case near the touch pad went closer to the upper case.  When I held the MBA with my right hand near the hinge and the power on key, I could hear clearly multiple knuckle cracking noises.  I went back to the Apple Store, and the technician said it was normal because it's re-opened after factory assembly.  Eventually they re-screwed the lower case but no improvement was made.
Has the case been bended or damaged?  It's still under AppleCare so what can I do?

Answer 1

Yes, it's an Apple Store in Sydney, Australia. 
I brought the MBA to another Apple Store and a guy there found the loudspeaker on the left side could not be aligned properly and there were other things inside to be re-aligned.  He also pointed out a dented corner on the keyboard side upper-left corner (not the lower side) and a few punched edges near the ports on both side and a number of scratch marks on the top (Apple Logo) and the bottom.  They were all new and not found when I took the MBA to the Genius Bar two days ago.  (Before giving the MBA to Apple Store, there was no scratches or damage as inspected on the spot.)
I thought my MBA had been dropped to a hardground at the first repair service in the Apple Store. I could not think of anything otherwise.
b.t.w. It was initially a non-recoverable Verify Disk problem as reported by the Disk Utility 10.8.3 and the SSD could not re-install OS X either. That's the reason of my first visit to Apple Store.  When I took it back, I found that I could not make the Recovery Disk USB and by Option restart, I found no Recovery Volume. That's why I took the MBA back to the Apple Store and asked them to re-install OS X properly.  Over there, I also showed them the click and crack noise.  The tecnician said he was very sure that my Time Machine backup was corrupted and thus during the restoration, the corrupted TM backup erased the Recovery Volume!  (I don't believe it.) I took out the TM backup external HDD and immediately inspected it with Disk Utility, there was no problem.  And later I restored the same TM backup to the MBA with no problem, and the Recovery Volume was there.  I don't know why Apple Store opened the MBA's case when it was only an OS issue.  and I cannot understand why a software issue will make my MBA's alumnium case clicks and cracks forever with dents and scratches everywhere!