Thanks for the additional information - this notification did come through Marketo and referenced a Salesforce Sync Error:
Our Marketo API looks similar to yours with only 9 requests in the last 7 days.
I have a feeling this might be the result of some testing that has been occurring this week for a (potential) new service we may implement. I do have a campaign running daily to overcome a a blacklisting incident mid-last month to re-activate leads that "wake up" with activity - however, this is a small number in comparison to our limits and our database (about 7000 leads are contained in that campaign).
Completely agree with the latter points about increasing limits - I don't think this is going to be an ongoing trend but we will see what happens with this potential new service and go from there.