I would say you need to return those headphones...sounds like you got a bad pair...I have the x4's more than a year ago, which are very similar and have not experienced any of those issues. you should never hear popping with your headphones. The only thing you probably should hear is a slight static (white noise) when there is no sound present. That is more a issue with the wireless nature of the headphones....the price you pay for wireless.
The hissing when you talk is also not right...should be clear audio...
Sorry to tell you that you need to return... I hate having to return stuff.
I read in another forum some people were hearing popping due to not having the controller cable plugged in all the way...I read that here
http://forum.teamxbox.com/showthread.php?t=637504&page=3
Question: do you have a lot of other wireless devices in the room that you use your headphones in, e.g., cordless phone, wireless hdtv, wireless printer, etc.?
Hope that helps