I can't do noises, I can't tell you how to find them. You or someone you hire, must find the noise before you can fix it. If it is an engine noise, it could be a bad lifter, a broken valve spring, a bad rocker, a loose valve guide, a bad oil pump or a bad oil pump pressure relief valve, a bad cam bearing, a bad crank or main bearing can all cause noises in the valve train. But some very unusual noises can be caused by bad harmonic balancers, broken flexplates, bad waterpumps and alternators bearings, bad fan clutches, blower motors, A/C compressors and believe it or not, paper stuck in the grill.
A good tech will perform a bunch of tests to determine what makes the noise come and go. The tech may test drive the car if the noise is related to brake application or steering input. If the noise is an engine noise the tech may kill each cylinder one at a time and listen to the noise and see if it changes. If it does, the tech will know which cylinder is a part of the noise and of course, which ones aren't. We often use a stethoscope to find the area of the engine the noise is coming from.
Once the noise is isolated to a particular part of the engine, transmission or rear end, the next step is to take an oil sample and look at it or have it analyzed. Sometimes you can see the metal in the oil and sometimes you can't but a local oil lab can see what kind of metal is in the oil. Aluminum typically comes from the pistons, brass and lead from the bearings or the radiator, steel from the crankshaft and often times water or coolant will be found which will tell us a coolant leak either started the problem or was caused by the problem.
It is very important to find the true cause of the failed lifter or failed bearing because their failure is almost always caused by something else.
The most important thing is to make sure you are working on the right noise. I can't tell you how many times a transmission was overhauled because the driver thought the transmission was stuck in second gear when the fan clutch was locked up. Broken flexplates or flywheels sound EXACTLY like a bad rod or main bearings and the two are very hard to separate. The difference between the two is when the symptoms occur and what makes them come and go.
Knowing that, you see how important it is that the driver clearly tell the shop how and what makes the noise occur and what makes it go away. The drivers involvement is critical when hunting down a noise. And the good news. Sometimes a huge piece of carbon will break loose from the EGR passageway or from a valve and it will end up sitting on top of a piston. It will make a huge knocking noise, a noise so loud and so bad that everyone who hears it will think the engine is going to blow up any minute.
We can dribble ATF or water into the engine through the carburetor or the fuel injection throttle blades and cure that "knock" in one minute and at a cost of $25-125. I learned this years ago when we diagnosed a knock as a bad engine and the customer went to another shop and they decarbonized the engine and cured the knock. You can imagine how mad the customer was when they came back to us to tell us that they got the knock fixed for $60 not the $4,000 we had bid the repair for. So as you can see, noises are sometimes very difficult to pinpoint.
So when you have an engine noise, check or change the related fluid and do your best to find out what makes the noise come and go and which portion of the engine it seems to be coming from.
Here's a few words we recognize as noises and what usually cause them:
Bang -- Backfire caused by spark misfire or lean condition
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