My truck has made a tapping noise for a long time. I initially had pulled the valve cover and, to my surprise, the timing chain guides were fully in-tact and valve adjustment didn't appear to be out of spec.

Further troubleshooting led me to the power steering pump and alternator area. The noise is more prevalent there. I decided to pull the belts and see what happened. So I pulled the power steering pump... no dice, same noise was present. To my surprise I pulled the alternator belt and fired it up... NOISE WAS GONE and the motor purrs like a kitten... super quiet.

I have never heard of an alternator making a noise like that. Squealing? Yes. Not a weird intermittent tapping. The noise increases with RPM but it is not a consistent tap that would be normally associated with valves. Then again, it could be the water pump. My belts are also dry-cracked and on their last leg.

What is odd is that when I free spin both the alternator and water pump... the bearings feel fine. I cannot tell there is an issue unless the motor is running. It is always there regardless of engine speed or temperature.

Has anyone had this issue? Is there a chance it is just the belt? Before I go dumping any money in it, I figured I would check with the forum here.

 

Don't guess test!

You can try a mechanics stethoscope, but in this case a long wooden down (dowel!!) will certainly keep your squishy bits out of harm's way.

Edit: please do not hold a duck to your ear and shove it into your engine bay, while it's running..

 

Down? From a duck?

I've had success using the paper core from a roll of paper towels. You're a little closer to mayhem than with a long dowel, but less likely to poke your ear out should the engine shake.

But try one of them. Otherwise, you're guessing.

 

DowEL...
Damn auto-complete. LOL! (I turned that off on my smartphone)

That technique worked well for my rear axle bearing diagnosis.

 

That is a great image RAD(Ray) the squint is good but your tongue angle needs some work..

The cone/tube does well for isolation in a directional sense, you can improve on this isolation with the stethoscope or a rod. The rod will cut out some of the random rebound. The stethoscope effectively puts your ear drum against an object. You can start with a tube and isolate left of engine bay versus right of engine bay. Once you have isolated a side you need to put your ear on to the parts on that isolated area, this is where the rod or stethoscope comes one.

 

Scope brings up a good safety issue I have never considered. If you are using that long handled screwdriver as a extension for your listening device you should put the pointy end on the object you want to transfer sound from.. Much like the cotton swap don't put pointy things into your ear.

I typically (I hope?) remember to mention to put the rod against the object, your thumb against the rod, and then the thumb against your ear. This protects your ear drum by preventing piercing of the diaphragm and lowers the amplitude of the sound.

 

Someone on this forum (RJR?) pointed out that some noises (eg, exhaust leaks) aren't really transmitted through solid parts anyway. In those cases, putting a solid rod against, oh, the exhaust manifold doesn't improve matters. There you'd want to use a paper towel roll or a piece of large-diameter fuel hose.

But for alternator v. water pump, a solid connection might give you more sound.

 

Thanks guys, I should have mentioned that I do have a scope and I checked every component on the motor top and bottom - cannot find the noise for the life of me which makes me even more suspect that it’s something really dumb like a belt... can’t scope that... The noise is just so darn odd to be coming from what I narrowed it down to...

 

I decided to go the ‘buy everything on Amazon and return what I don’t use” route.

Belts need replaced regardless so I can start there.