That does sound like it may be overheating.  Use MSI Afteburner (or something similar, like GPU-Z) to monitor the heat and overall system health.  Even without overclocking, heat can be a big issue if your system isn't properly ventilated or cooled, because mining stresses your GPU to the limit (it's like running a burn-in test constantly, 24/7).  If it turns out your GPU is getting really hot (anything above 80 degrees C is not recommended), then you can do two things (doing both is a good idea): first, use MSI AB to set a "thermal limit".  This will tell the GPU to automatically throttle back, if needed, to keep itself under the temp limit you set.  Second, add more system fans, or replace old/worn ones.  You can also rearrange things as needed, to give your system more "breathing room".  Some people with dedicated mining rigs don't even use a case, and have their GPUs very open to the air, for maximum ventilation/cooling.  If you use your system for anything other than mining, this is usually not very practical. lol  But in any case, do try to maximize the amount of air your system gets, to keep it cool.