What this is mainly sounding like is neighboring wifi inteference, you aren't really providing enough info to troubleshoot this further, such as what mode are you running in - G/N? are you using HT20 or HT40 wide mode? How close is, if any, neighboring wifi's and what channel are they using and what channel are you using? Also, WPA2 personal with AES is all you should use as its the most secure.
And for the record, you can RMA till you are blue in the face, even purchase a different unit, but if this is infact wireless inteference, it won't matter because you'll face the same problem everytime.
