ok mookshoe commenting on the engine issue only as the other is not in my range . it sounds like you are dragging a piston ie for some reason one piston is not firing normally i.e the piston is not getting a spark .is not getting fuel. the cylinder is faulty because of ring damage or faulty valves.and there is an outside chance that it can happen from a faulty head gasket .the reason it sounds a little smoothe when you increase the revs is that the other three cyliinders are driving the engine at such a higher rpm that miss becomes less pronouncecd ie less noticable but is stil therer in esscence or partially there and has begun to fire at higher reves because of better compression or intermittent spark getting thorught .either way your engine needs quick attention as if left as is can result in permanent damage .I would have the cylinders pressure tested immediatly.and the plugs tested or changed out anyway.but the pressure test shuld show up abnormalitys in the firing on the cylinders esp..if performed on running engine by a competent mech,s