My Viking has a strange knock in the engine, or what seems to be coming from the engine, mainly when cold. It happens right after I start it and as I put my foot on the accelerator it goes knock knock knock then as the revs pick up the knock disappears. Has anyone else noticed this? The knock seems to be worse the colder it is and this morning it was our first cold morning this year, 5 degrees C, and the knock was quite loud. It only does it as you accelerate from idle and nowhere else in the rev range. Any ideas anyone? Just to give you an idea it sounds like a big end knock which no doubt it isn't.