I started another post on this same issue about a week ago. There are already some responses in that post that you can look at, however, I can tell you what I have found and done so far that has resulted in no changes whatsoever.
http://www.buildlog.net/forum/viewtopic.php?f=33&t=2301-Replaced USB cable with 1.5' shielded usb cable with ferrite core.
-Replaced power supply twice. Currently running 24V 18amp power supply from Meanwell. Running heated bed as well.
-Checked hot end and heated bed connections. Even hardwired them directly to the Azteeg X3.
-Tried adjusting settings in Repetier Host (Baud Rate, Cache Size, send and receive options)
-Tried running repetier host from both newer PC and Mac. Mac performs better but same issue happens eventually.
-Run directly from an SD card.
-Tried Pronterface
-Ran different STL Files
-Ran the machine with no heated bed or extruder setup in Marlin.
-Checked PC for all energy saving mode. I even stayed active on the PC and saw it shut down.
-Tried multiple outlets in the house. Plugged the machine into its own outlet and plugged it into the same outlet that my PC is connected to. In both instances I avoided turning on or off any electrical devices on the same circuit.
-Just replaced extruder motor.
These are all the recommendations I have seen from multiple websites from around the internet. You may have luck with one of those recommendations, but I am still having the issue and I have had my printer for around 4-5 months now. I saw in the post for the Azteeg X3 that one of the users bypassed on the onboard FTDI chip on the Azteeg and is using a straight RS232 serial connection. I am in the process of trying this. I have had to purchase a PCI express serial board from Newegg and an RS-232 to TTL converter from Sparkfun. I am not even sure how to hook it up correctly, but I am running out of solutions to resolve this problem. I hope you have better luck than I have.