I've seen that area before, unfortunately there isn't much distinction between functionalities that we use.
By "distinction" you mean all your API users are evenly dividing the API calls, and all of them equally increase when you send, to the point that limits are exceeded?
What are all the different integrations you have running? Something is just not right here.
With distinction I mean, what Greg referred to earlier, users per application.
Right now 95% of the calls are with one user. As I haven't setup the the instance I don't know exactly what is happening and why.
My next step is to sort out if and what we are sync(ing) and how this is done... Will get back to you guys as soon as I have more details.
One first sanity move you can make is to have the various apps using the API to use different Marketo API Only users. This will enable you to track who is faulty one.