mintMenu falls back to a rather inefficient way of monitoring filesystem changes in the absence of the pyinotify Python module. This causes mintMenu to produce a small but not insignificant CPU load continuously. This matters especially on laptops on battery power. Installing the python-pyinotify package and reloading mintMenu fixes the problem. I suggest that the mintmenu package should have python-pyinotify as soft or hard dependency, and it should be on install discs that include MATE (it's a tiny package).
I observed this on the latest LMDE, I'm not sure if the Ubuntu based editions are affected but I suspect so.