Uh-oh! Ominous knocking sound from front end - advice? (1 Viewer)

[Adam R]

I've had a similar, very intermittent, tapping as well. Sounds like a baby woodpecker is tapping away somewhere in the engine bay. Only does it when I have no chance of jumping out and popping the hood see what/where it is coming from. I only notice it when I'm driving very slow or coming to a stop. It's been doing it for years and I still do not know what's causing it. The vehicle runs/drives fine so I just press on hopping to catch it in the act at a future date.

Adam

 

[buddysharp]

No loose steering components. Noise only happens at idle. Not sure how ujoints impacted as the vehicle is at dead stop?

 

[VtaTom]

Maybe this is turning into a mystery noise thread but I have an intermittent noise from somewhere up front too. It only happens when it's colder than 45f and the engine is just coming up to temperature and I have just stopped.
It sounds like a pan with eggs boiling or a rattle and it only lasts a few seconds.
I suspect the engine is tilting and the noise stops once it settles. I'm going to try taking off the plastic engine cover to eliminate that. That's the only thing I can move by hand.

 

[Trunk Monkey]

I'm heading towards something like an exhaust bushing being toasted. You've got a harmonic going with something. Sitting in idle the tranny isn't moving, so it shouldn't be anything in there. Shifting out of gear changes the RPM slightly and maybe enough to stop the harmonic. My plastic engine cover thing does it from time to time. Stop at a light one time and it starts rattling, enough that pedestrians will look at the truck like "wtf?". Next light, nothing.

 

[LX101North]

Isn't the drain plug on our transmissions magnetic like they are on the diffs? If I thought i had metal on metal contact coming from my transmission, I would do a drain and refill. And if your fluid is still good, reuse it. I don't know much about this stuff, but you would think that there would naturally be a greater amount of debris in your pan.

 

[semlin]

No loose steering components. Noise only happens at idle. Not sure how ujoints impacted as the vehicle is at dead stop?

did you look at the rack while turning the wheel? when the rubber mounts go you get play. mine lifts about a half inch when i turn it.

ujoints are still under load when you are in gear and you say it goes quiet when you go in neutral. when a ujoint went on my 80 they rattled like crazy at idle at intersectiions and at very low speeds but then went quiet when i sped up. took me a while to find the noise.

 

[Glacierskier]

Noise

OK, I had a similiar noise that appeared the other day. Scared the @#$% out of me. Sounded like a 18 wheeler using it's engine brake off in the distance.

It has been dipping below -10° every night and only happened in the AM, when still coldish and when in drive. This AM I found the source. I started it, ran till warm and RPM's dipped to about 800 and I parked the 100 against the edge of my garage(so it would not kill me), popped the hood, ebraked it and put it in drive. The RPMs dropped to about 650 and the noise began. Had a look and it was the engine shroud vibrating against the oil filler pipe. I hope you are as lucky!

 

[Elijah]

Could definitely be it. Good job on finding that and thanks for posting up for future reference.

 

[2001LC]

Keep and eye on idle for reference, since when braking the boost pump comes on only sometimes and it dropping RPM a hair. Low idle seem common too your issue, just as brake and in gear do.

I could not hear the YouTube sound very well. But it did sound like a pump. I could not hear the metal on metal sound you report. Hopefully you can post a better recording.

IIRC you did not flush power steering, I'd flush it and all 12qt of transmission. I like Mobile 1 synthetic ATF for both and its found in most parts stores. If all else checks-out: mount (engine, trans & exhaust), MAF meter cleaning, T-body throat cleaning, air filter, and put some 44K in gas and don't forget to reset ECU, etc.... in other words a general tune up and inspection.

As a good mechanic once said to me; "sometimes you just have to wait until it breaks".

If sound stop recurring, no reason to concern your wife with that little detail just keep driving.

 

[buddysharp]

Well tuank you all for all of the help. Good news is I used this as an excuse to do a butt load of deferred maintenance and found some worn out bushings here and there, a cv boot thats ready to be replaced, a clean front diff drain plug with a bad crush washer, front wheel bearings desparately in good shape, u joints in decent shape but with more play than they should have, a tight steering rack, a leaky front shock, and a cracked engine cover mounting point.And, a pretty rough idle when in gear at a stop but only noticeable if you put ur hand on the engine.

All that and out of desparation I tried to climb in the engine bay with long screwdriver in hand, put muyhand on the front corner of the engine cover and... discovered I'm a friggin moron. Voilà, the sound appeared for a split second. Yep just the right amount of pressure pushes the cover close to the oil filler tube and damned if it doesn't sound like metal on metal. Talk about tricky harmonic.
Thanks to ALL for the suggestions and thoughts......including the humor!

 

[SWUtah]

Well tuank you all for all of the help. Good news is I used this as an excuse to do a butt load of deferred maintenance and found some worn out bushings here and there, a cv boot thats ready to be replaced, a clean front diff drain plug with a bad crush washer, front wheel bearings desparately in good shape, u joints in decent shape but with more play than they should have, a tight steering rack, a leaky front shock, and a cracked engine cover mounting point.And, a pretty rough idle when in gear at a stop but only noticeable if you put ur hand on the engine.

All that and out of desparation I tried to climb in the engine bay with long screwdriver in hand, put muyhand on the front corner of the engine cover and... discovered I'm a friggin moron. Voilà, the sound appeared for a split second. Yep just the right amount of pressure pushes the cover close to the oil filler tube and damned if it doesn't sound like metal on metal. Talk about tricky harmonic.
Thanks to ALL for the suggestions and thoughts......including the humor!

Very cool, every time I read about 100 series problems most of the time it's something minor. Glad you found it.

 

[Elijah]

Well tuank you all for all of the help. Good news is I used this as an excuse to do a butt load of deferred maintenance and found some worn out bushings here and there, a cv boot thats ready to be replaced, a clean front diff drain plug with a bad crush washer, front wheel bearings desparately in good shape, u joints in decent shape but with more play than they should have, a tight steering rack, a leaky front shock, and a cracked engine cover mounting point.And, a pretty rough idle when in gear at a stop but only noticeable if you put ur hand on the engine.

All that and out of desparation I tried to climb in the engine bay with long screwdriver in hand, put muyhand on the front corner of the engine cover and... discovered I'm a friggin moron. Voilà, the sound appeared for a split second. Yep just the right amount of pressure pushes the cover close to the oil filler tube and damned if it doesn't sound like metal on metal. Talk about tricky harmonic.
Thanks to ALL for the suggestions and thoughts......including the humor!

Lol, I was about 99% positive it wasn't anything serious. Glad to hear it wasn't any of those crazy things, you can sleep peacefully.

 

[2001LC]

I love it a plan comes together the "D" team

 

[southerncruiser62]

I second the engine cover as the issue. I had the same issue this weekend and pulled engine cover off only to find the foam/padding that should have been on drivers side cover at oil fill location had come off cover causing it to rub and create harmonic exhaust rattle sound. Quick clean and small strip off weatherstripping took care of problem.

 

[gwatts]

3x the engine cover!

Was getting this noise as well. Sure enough, it was the engine cover. Drivers side cover at the oil fill location.

 

[boobird]

Very happy to find this thread. Got the same jackhammer noise. Will check the engine cover.

 

[AirMax10]

very helpful info. Thanks!

 

[vwhammer]

Well, allow me to be the next person to bump this old thread.
I have the same noise and just read through this thread hoping for an answer.
I have not actually checked mine yet but you can bet that I will scope it out in the morning.
I was not too worried about mine because it just sounds like maybe an exhaust thing clanking on something and it only does it for a few seconds and stops but if I can fix it great.
Fingers crossed...