I have a 2010 scion xb. A few months ago it starting hesitating after you slowed down and start to accelerate. There a rrrrrrrr noise l right under your feet when it hesitates. When you give it more gas e hesitating stops. I've changed the plugs and coil packs. The only thing I've noticed different was a little oil around the first plug. I know that's the gasket though. Anybody have by clue to what could be doing it? Thanks.