Are you loading up any patches when it starts or are you starting it without any patches loaded? If it is a patch that is causing the problem, you could try starting with the -noloadbang flag. Also try starting it with -noaudio flag to see if it is indeed the dsp that is causing the issue. Also, check to see if other apps are causing similar behavior. I have worked on a few MBP models from 2012 recently, and it would seem that planned obsolescence is right on schedule, as there was a wave of 2011 and 2012 models having their GPUs spike performance and overheat late last year. Thats a long shot, but hell if I havent seen it with my own two eyes...
https://www.cultofmac.com/262861/early-2011-macbook-pros-dropping-like-flies-heat-issues-blame/
If that is relevant, try taking measures to ensure that your laptop stays cool and well ventilated. Even when the GPU isn't failing, overheating of the GPU causing those sorts of behavior is fairly common in MBPs from my experience.