1995 Buick LeSabre-There is a loud metallic knocking sound. I took off the serpentine belt to see if one of the pulleys had a bad bearing. It wasn't that. It sounds more like it is in the back and center of the engine, if you are looking at it from the front of the car. It does not increase or decrease with rpms, which makes me think it is not internal. It sounds like a something in a fan.
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Turn your A/C off, the compressor can make noise if bearings are dry or system is low on compressor oil. Remove your serpentine belt. Turn pulleys by hand to check for roughness. Bearings in those pulleys routinely go bad. You may get computer warnings with the following test, but with serpentine belt removed, run engine for 2 or 3 minutes. Do this on a warm engine after serpentine belt is removed. The warm oil will not mask the problem like cold thick oil can. Noise generated means problem is internal. If this is a stick shift transmission sometimes the clutch bearing can make noise and is a sign that bearing is bad.
Hello: Remove the serpentine belt, see if the waterpump pulley wobbles/makes noise when you spin it. If thats not it then start the engine, belt still off see if noise is there also while engine is running see if vthe crankshaft pulley wobbles. Also check the A/C compressor pulley (engine off, belt off) spin it by hand and check for noise and wobble. If all the previous is ok then it could be the balance shaft front bearing and or the timing chain.
You might just need a fan bellt or serpentine belt, get an empty spray bottle mix a small amount of
dish soap and water, spray on belt, then start your engine if the noise stops just replace your belt.,
if it does'nt it could be another pulley or the tensioner pulley, then i would suggest removing the belt
and spin each pulley to determine which one is making the noise. if it turns out to be the alternator, you
will have to replace the whole thing. they don't normally sell just the pulley, and even if you can get one
requires special equipment to pull it off, if needed just replace it and save yourself time and trouble.
plus parts normally come with some kind of warranty. good luck!
it could be the tensioner, water pump, alternator, A/C compressor, power steering, or even a really bad serpentine belt. The only way to be sure is to remove the s-belt and spin-check the pulleys and listen for squeaks or grinding bearings.
noises are difficult to track but since your's is on top, try this-CAREFULLY use a wooden handle (from a broom, or paint roller extension) and place the end against items on top of the engine-the other end, your ear. Be aware of the moving pulleys and the belt, take your time-you can isolate the noise this way, and plan your next step.
Tell somebody to rev the motor and check where the problem is from, otherwise remove serpentine belt, if it's a supercharged model remove supercharged belt before, and remove the accessories belt ! tell him to start the motor a short time to see it the knock sound is there or not, if not check each pulley if there's any loose or strange noise while turning them !