guys, sorry for the offtopic.
Yep, the popping noise as well. I've bought a pentalobe screwdriver from ifixit, and tried to tighten the screws properly. Didn't solve the problem, but messed up the heads of the screws - the screwdriver doesn't turn them anymore.
I've thoroughly researched this matter and found out that the screws should be put in a special order (the peeps here at macrumors helped me to find the whole macbook air technician guide, here's the link:
http://is.gd/A30Ga3). So I ordered original replacement screws through ebay and plan to make it good this time, using the guide and the new screws. If it won't help - I'll take it to the Apple Service Center once again and ask to replace some parts or the whole computer (the first time they tightened the screws and made the creaking slightly less evident, but didn't solve the problem completely).