Thanks for all your replies, guys.
I mentioned this topic in conversation with Tideace representative. Of course it's not worth sending the frame back, given that a new one would be about $250. But anyway, it seems that according Tideace warranty rules I must return my frame first.
It's very convenient for them, I think, because nobody will return a broken frame back to China and pay shipping taxes and wait who knows how long if they can get a new frame for just another $250. Sure, it's not big money, but it's not about the money, it's about how all this "warranty" thing doesn't really work this way. I wonder if there was anyone who ever sent his frame back to China for rapair)))
As far as I know, Tideace representative was going to register on this forum. So I hope he will speak for himself now.

Hi, guys!
I need your opinions regarding my situation.
I bought Tideace fm-m015 29'' frame about a year ago, built my bike on it, and was really happy) A month ago I found its BSA bottom bracket shell quite loose in it's place and making creaking noises. Store offers 2 years warranty, so I took some pictires of the problem and sent them to Derek from Tideace store. He said they can see the problem and I need to send the frame back: "you can ask others. if their frame was broken or they want to replace new one. they should return the parcel back to us firstly". But i'm not sure about all this sending back thing...
He said I could ask others, so i'm asking: is it really how the frame warranty works? Did you have the similar situations and how was it solved for you?

Thanks!