I suddenly have this rattle noise whenever the engine is running but it diminishes with speed. It almost sounds like spark knock but spark knock would get worse at speed. It could be the water pump. Would a water pump get louder with speed, or go away as this does? I feel a tiny bit of in-out motion in the shaft but not side to side. Car is a Geo Metro and does have hydraulic lifters.
check your belt tentioner , ten-shun er. the computer keeps telling me i spelled it wrong
sounds like a pulley or bearing noise
Its possible go find yourself a four foot piece of hose and put it right on top of the water pump with the car running and stick your ear to the other end. you will hear the bearing if its going bad, it could also be the alternator, but, if you have a Serpentine belt odds are its the belt tension er and this thing goes bad often. If it has a belt tension er, may as well replace the belt too. good luck
