New longboards can suffer from squeeking when turning. Most people assume it's coming from the bushings. The noise is coming from the pivot cups, which is an indentation on the baseplates of the longboard trucks.
There are a number of remedies including soap, pencil graphite, candlewax and olive oil. To fix, you need to strip down your longboard trucks, put your chosen remedy into the pivot cup, then reassemble the trucks.