Beta Testing: Phantom hills

I am finding "phantom" hills when I apply elevation.  Hills that I know just aren't there. I can ignore this on routes I know but how do I plan a ride on a new route.  Another interesting thing is that one route I tried seven times, Most of the route was OK but at 3km and 5km there would sometimes be hills and sometimes not, and the when they were there they were different sizes. Does anyone how the elevation points are obtained. I download the information to Excel, standardise the distances and then put them into charts to compare new routes to those I already know.