I seem to be having the same issue. Sourcetree keeps becoming unusable (after a few minutes/hours using it) and starts using 95% cpu, I see the flickering of "Push changes immediately" and I see lots of command line / git processes, although I see at most four (maybe they simply go away faster because of my virus scanner doesn't interfere).
The repository where this happens isn't big at all. Its tiny and new.
I'm running 2.4.8.0 on Windows 10, with (this might be important) Visual Studio also running on the same folder with its own git integration.
Refresh automatically when files change is always off (as that never works). But still Sourcetree seems to be doing 'smart' things in the background.
Going to downgrade to v.2.3.5.
neoscorpe we have made some changes to this in the current 3.0.0-beta. It would be useful if you were prepared to test this and see if it improves your situation.
The beta tries to run in a sandboxed way, using its own configuration files, e.g. bookmarks and accounts, but when opening the same repository it will change some of the per-repository configuration so it is worth making copy of problem repository and opening that with the beta.
The installer can be downloaded here: https://bitbucket.org/atlassianlabs/sourcetree-betas/downloads/
Alternatively closing all tabs a part from the problem one then opening the Tools/Process Viewer and reproducing the problem will list all the git commands being run, that information can be exported. If you exported that and, after doing a quick sanitization, posted it to the issue that would help.