If you haven't already, go to VIEW>Mix Window Shows>check the Delay Compensation option. This will add a row of info across the lower part of the MIX window. If you see numbers in those lower windows, they will show if any delay compensation is in play(and if it IS, that's the cause of your echo/latency). With no plugins in play, bogus delay comp can be caused by 2 things; #1-routing audio thru cascaded buses. #2-any track with a send that feeds no destination(like if you added a send to another track, but then deleted the other track, so the send is causing ADC confusion)