Even when my car is on the motorway, under acceleration, it sounds like a tractor. I'm used to this noise when the engine is cold, but not when it's been warmed up. Additionally, when starting the car first thing, it vibrates heavily, sounds like it's just firing on a few cylinders. I understand that with this freezing weather, the oil will be a bit thicker, but I'm still reasonably certain it shouldn't shake like it does. Any suggestions?