Something to consider is also what other things are plugged into the same service that is driving your modular. Is your modular plugged into the same service that you're using to record or listen back?
There is the lengthy process of unplugging all of your modules and then listening to them plugged in one at a time and adding them to the modules marked "safe." If you power on with one module in each rack and there's no whine, then it's probably a module or multiple modules that are causing the noise.
Digital modules, especially those with LED or LCD screens can give off some nice amounts of noise. So work with the purely analog modules first to rule them out.