Name that noise

Steve777 · **Joined:** Fri Oct 16, 2015 11:31 pm **Posts:** 279

I have been noticing a noise from my 06 CRD for some time now. Done a little "playing around" to see if I can narrow down what causes it and doesn't, and I think I have gone as far as I can, and wanted to get some input from folks here. (Caveat, my hearing is poor so feel free to suggest other things/sounds that maybe I "should" have heard)

The noise is basically a faint to moderate tapping, in time with engine rpm. Not as hard/sharp as a loose mechanical lifter/tappet noise, but sort of a muffled version of that. It seems to be faintly present at idle. Very present at 1500-2000rpm with light go pedal pressure. And goes away when I press on the go pedal more. It seems be present only when little to no power is being requested.

It seems that if I quickly take my foot off the go pedal when the noise is happening, then the noise stops immediately, even before the rpms go down. From this, I was leaning towards this is an injector noise that is happening at certain lower fueling levels. But I suppose it could be valve train related (like a loosening tbelt or the like) too.

Anyway, I was hoping this description might sound familiar to some of the experts here, and give me an idea of what to look for.

TURBO-DIESEL-FREAK · **Joined:** Sat Apr 17, 2010 3:29 pm **Posts:** 1167

Any chance that it may be the alternator decoupler pulley?

Is your serpentine belt vibrating a lot, and do you see your serpentine belt tensioner jumping around a lot?

I know the noise of an ADP rusting out and malfunctioning to be different than you are describing; ADP noise is more of a rattle and/or a chirping sound. However, you did say you had hearing issues.

WWDiesel · **Posted:** Wed Dec 26, 2018 11:51 am

Check harmonic balancer on front of engine. Make sure it is not coming apart where the rubber is bonded to the metal.
There have been several members who have found theirs failing and making a rattling noise similar as you described... :banghead:

Steve777 · **Joined:** Fri Oct 16, 2015 11:31 pm **Posts:** 279

Thanks.

Should not be the alt, just replaced that a year or so ago. But hey worth checking again. Will also look at the serp belt and see if it is bouncing around.

Likewise will check the the harmonic balancer.

Also sent in an oil sample, so in a bit should know what that looks like.

rankom · **Posted:** Wed Dec 26, 2018 3:58 pm

also if you can , it will be good to install T fitting at oil pressure sending unit and put in mechanical oil pressure gauge , run engine to operating temp, and record oil pressure then add some lucas oil stabilizer , not to much ,then check oil pressure again , again at operating temp . see if any difference.

mrhemi · **Joined:** Tue Dec 08, 2015 10:46 am **Posts:** 180

Anyone have any idea how many mile a replacement Litens alternator decoupler pulley would be expected to last? I have a similar noise developing. It is coming up for a second timing belt change, so will look into the balancer as well. I replaced the decoupler 3 years and about 90000 miles ago.

GordnadoCRD · **Posted:** Thu Dec 27, 2018 6:51 am

If you haven't found it after checking all of the above, take a look at your exhaust manifold.
Specifically, a failed exhaust gasket between head and manifold,
OR
a cracked exhaust manifold near the exhaust port.

At this location, individual exhaust pulses would be audible as a tick noise, but under heavy throttle they would fade to a hiss as exhaust pressure increases. Possibly even supersonic noise.
When removing foot from accelerator, pressure would immediately fade and no exhaust "ticking" would resume until the engine is again idling against the torque converter or low accelerator pressure is applied.

Name that noise

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