Jeff nailed it.
Are you still working with a Marketo Enablement Consultant? If so, as him/her about setting-up your sync to SFDC in a Sync or Lifecycle Campaign.
There are two philosophies on when a lead should be synched:
1. Sync all leads to SFDC immediately, but hide them from sales until they become Marketing Qualified. Advantages are that leads can be de-duped on the SFDC side, and reporting will be aligned between Marketo and SFDC. Downside: You have to provide sales with a filtered view of the leads, or they will start going after raw leads.
2. Hold back leads in Marketo until they are MQL, then sync. Advantages are that less leads are in SFDC, less sync traffic, no SFDC processes can be triggered by accident, and without changes in SFDC, sales only sees MQL. Downside: If you are synching Marketo Programs and SFDC Campaigns, leads will make it into SFDC when they first become a Program/SFDC campaign member, regardless of whether they reaced MQL status.
I much favor option #1, as it is simpler and cleaner.