It never stops, one thing gets corrected and everybody is happy until the next mystery shows up. The 1999 Dodge Cummins 2500 was doing great once the fuel leaks were taken care of. After a few days my brother called me and mentioned a strange harmonic sound coming from under the hood at start up and then fading out once he started to drive. Well the sound has gotten worse and louder. He sent me a recording of it that I could hear with ear pods from my phone. It sounds like a tuning fork. All the belts are good, the belt tensioner is good, fluids are correct, no clamps loose or tears in the boots. I went online and put the description in on google and had some similar sounds but mostly on gassers with no explanation of where the sound was coming from. My hearing is poor and my brother's hearing is worse. We both wear hearing aids but you can hear this harmonic sound plainly. I don't know if I can get another recording to attach but I will try. He parked it at home in Columbia, S.C. because he is working out of town. Any suggestions will be appreciated, I have never heard a sound like this one but maybe some of you have. Thank you

Have you tried disconnecting the fan belt and then start it to try and isolate the noise ? 

I would be curious to hear the noise, becouse I had a similar issue a couple days ago in semi truck, a harmonic type sound developed all a sudden, but it ended up being fatal for the turbo.

No, I didn't think of that. I'll pass it on to my brother. He sent his turbo to be rebuilt, something I would not have done unless I was certain it had an issue. It came back with no issues everything was fine. A learning curve for him $$$$$$$ to remember. There is no point guessing or replacing parts unless you have some deep pockets. Thank you for your advice and have a great day.

I don't know if you can hear the harmonic sound on this recording without a headset but when the truck is first started up the sound is apparent. Maybe this will help identify what's going on.

New Recording.m4a

I noticed recently my fuel lines were the cause of what I thought was tappet sound from under the valve cover. It was metallic/harmonic. Needed to put a few of the clamps back on. Im talking about the brass colored metal ones that are all close to each other running from the VP to the injectors.

Edited October 25, 20177 yr by rogerash0

On ‎10‎/‎1‎/‎2017 at 11:36 PM, 01cummins4ever said:

Have you tried disconnecting the fan belt and then start it to try and isolate the noise ? 

I would be curious to hear the noise, becouse I had a similar issue a couple days ago in semi truck, a harmonic type sound developed all a sudden, but it ended up being fatal for the turbo.

You were right on the money, the harmonic sound stopped as soon as the belt was disengaged. I'm trying to get my brother to buy a stethoscope from Harbor Freight, it's only a few bucks and with his hearing as bad as it is I think it would help identify the noise. He said it was also making a ticking sound that was now loud enough to mask the sound. I don't know since the truck is not near me. The clutch fan seems to be working fine, the harmonic balancer has a little back and forth but it is the same on my 12v and the alternator turns freely. This is all with the belt off. I am against replacing parts when they don't need it and we have limited it down so I can't understand why it's hard to locate now. I'll let you all know when I find out some more information. Thanks again for the suggestion.

20 hours ago, rogerash0 said:

I noticed recently my fuel lines were the cause of what I thought was tappet sound from under the valve cover. It was metallic/harmonic. Needed to put a few of the clamps back on. Im talking about the brass colored metal ones that are all close to each other running from the VP to the injectors.

I'll pass this on too, he is complaining of a ticking sound that is loud and he did have his fuel lines apart. This is also a big help, thank you. I'll get back with you as soon as he lets me know something.

Harmonic balancers are not supposed to move sideways even with the belt off.

On ‎10‎/‎1‎/‎2017 at 11:36 PM, 01cummins4ever said:

Have you tried disconnecting the fan belt and then start it to try and isolate the noise ? 

 

On ‎10‎/‎29‎/‎2017 at 1:09 PM, Junkman said:

Harmonic balancers are not supposed to move sideways even with the belt off.

First, my brother did disconnect the belt and I don't understand why he couldn't identify the noise. He parked it for several months. Bought new alternator, water pump, power steering, and vacuum pump, you all need to understand that this is not how I would have gone about this and I expressed this to my brother. 

There were additional issues going on with the lift pump maintaining pressure and the computer on the firewall (can't think of the term), The harmonic sound was coming from the alternator bridge or diodes causing voltage spikes and drops. When the new alternator was installed it leveled out everything. Lift pump is holding same pressure, cruise control is maintaining speed, and mileage is back up. Great advice from O1Cummins.

 

Junkman I agree, I videoed mine running and it looks like it jumps around a little but no side to side. I look at the rubber between the 2 halves for damage.

I've got a ticking now too, me thinks it's the belt tensioner. A friend with a Cummins lost two belts; replacing his tensioner fixed it. I have not lost a belt, yet.

Whenever I hear a sound like that I give the tensioner a small shot of oil. If the sound goes away you've found the problem. Since I have had to replace belt tensioners more often than anything else on a old 12 valve I drove for 20 years, that has become the first thing  to do when there is an unusual sound. Never assume the worse with a Cummins its most often something simple. I put near 500 k on that same old engine

Edited February 5, 20187 yr by JAG1

On 1/31/2018 at 9:42 AM, Greenlee said:

I videoed mine running and it looks like it jumps around a little but no side to side. I look at the rubber between the 2 halves for damage.

 

The dampener should run smooth an straight. There are two alignment tick marks on the front that should match and line up. The outer hub is wobbling a bit its time to replace the rubber is giving way. 

8 hours ago, rogerash0 said:

I've got a ticking now too, me thinks it's the belt tensioner. A friend with a Cummins lost two belts; replacing his tensioner fixed it. I have not lost a belt, yet.

 

5 hours ago, Mopar1973Man said:

 

The dampener should run smooth an straight. There are two alignment tick marks on the front that should match and line up. The outer hub is wobbling a bit its time to replace the rubber is giving way. 

 

7 hours ago, JAG1 said:

Whenever I hear a sound like that I give the tensioner a small shot of oil. If the sound goes away you've found the problem. Since I have had to replace belt tensioners more often than anything else on a old 12 valve I drove for 20 years, that has become the first thing  to do when there is an unusual sound. Never assume the worse with a Cummins its most often something simple. I put near 500 k on that same old engine

I hope these sounds aren't contagious because I noticed a ticking sound I can't pick up on but it doesn't seem to effect the way it runs. I'm going to shoot a little oil on the tensioner as suggested, thanks for adding that.

My harmonic balancer does jump around a little, it's not easy for me to get down on the ground but I think you are right, it's time to replace it based on what you said on how it should run. When you don't deal with these types of things going on it's easy to second guess. That's one reason this Forum is so valuable.

 

I noticed a dragging sound when barely moving forward, almost like a bearing but it goes away once I speed up. It might be power steering, transmission, or maybe drive-shaft parts. I wear hearing aids but honestly, they pick up too much noise and it doesn't help pin pointing what's going on. I'll post it if I can find it but it might not be that important. 

I hope someone chimes in on that ticking sound as I have read it can be a sign of a bad injector. But then I think you have the kind of, not to worry kind of miles on that truck.

My injectors are brand new from F1 Diesel and put my old ones, and new DDP's to shame.