after doing some googling, i seem to be having this issue:
https://discussions.apple.com/message/27003600#27003600
i'll probably try reading through that thread and see if there are any solutions.
If it wasn't happening before you upgraded and it just started happening immediately after you upgraded there is a high probability that it has to do with the upgrade. The easiest thing to check is to swap out for the old ram and see if the issue stops happening.