Like the other poster said first port of call is to check the voltages, and then make sure the model 3 stack is seated well, so take apart the stack and re-seat it...
Run the video test in the service menu, that will usually tell you if there is faulty ram modules on the board...
If it fails the service menu test it is highly possible that it is a glitchy video board, which is a common fault on Model 3 stacks,........its worth swapping the videoboard from the working side into the glithcy side and visa-versa to see if that fixes the one side whilst visa-versa it turns the other side bad, if thats the case then its very likely the video board is faulty and glitching out....
There is someone on here who I have heard can fix them, I think his user name was "redleader" but that was a few years ago I saw that but it is worth seeking him out or alternatively you will need to buy a replacement videoboard if its faulty......