Does it do this when out of the case? If not, then it may be the way the case sits on it. It is possible that the case either really wasn't made for that device, or is flawed.
However, if it does this, no matter if in the case or not, then you likely have something on the tablet that is causing it. Bad app, virus, malware, etc. To check, try starting up the tablet in "Safe Mode" and see if it occurs in there. If it doesn't, then you need to check the tablet for what (virus, malware, bad app, etc.) is the root cause and then remove whatever it is. But, if it does happen even in "Safe Mode" (and while the case is off) then you may need to do a full "Hard Reset" of the tablet. Should that then not resolve it, then I would have it looked at by a tech (or the manufacturer if under warranty).
To get into "Safe Mode" please do the following.
1. First turn off the tablet.
2. Next press and hold "Power" until you see the manufacturers logo on the screen, then release the power button.
3. "Quickly" press "Volume Down" and hold it for few seconds until you see the message "Safe mode: ON" or something similar.
4. If you wanted disable it, simply repeat the steps above, and you should see "Safe Mode: OFF" rather than on.