Disturbing Noise

95 3.4, M/T, 4WD, 250,xxx miles. My truck has been making a strange noise for some time. Over a year. I can only describe it as sounding like the chain on a multi speed bicycle when you shift & the chain "hangs up" then moves over to the next sprocket. Like that only a deeper tone, if that makes sense. This noise occurs randomly, never when the truck is moving, once or twice when running but not moving, mostly when it is not running. A couple of weeks ago I was outside having a cup of coffee early in the AM the truck was parked near me after having sat overnight & the noise happened, then repeated after about four minutes. No work had been done prior to the first occurrence of the noise. Well after the first occurrence of the noise I had occasion to have the transfer case inspected & no issues were noted. I say this as the T/C is the only thing I know of on the truck that has a chain. I have tried to record the sound, but it happens so infrequently & so randomly that I have not been successful yet. Any thought, ideas?

 

Haunted by Jacob Marley?

Couldn't resist but I have nothing of value to offer here.

 

Very possible. Makes as much sense as anything I have thought of.

 

Does it make this random noise always at home or it might happen anyplace?

Interference back feeding through the speakers. Even when off!

Any sort of alarm or remote start anything controlled by a radio signal?

I have experienced that over the years.

 

Do you have any indication on where the sound appears to be coming from? So you're having coffee, truck is off, birds are chirping, dogs are barking, out of nowhere the truck makes a sound. Something electrical?

 

Seems to be coming from engine bay when I hear it when I'm in the truck. When outside the truck seems to come from engine bay or from under the truck. Doubt it is electrical. Sounds very mechanical. Sort of a grinding rattle. Sounds like something under spring tension unloading???

 

How hot or cold is the engine when you hear this? Is it moving at all or slightly when it does this? Very strange indeed.

 

I have had it occur while the engine is idling at operating temp and after sitting overnight in ~ 60 degree temps with engine off. As far as I can remember it has never made the sound while actually moving.

 

If it's a short sound I'd agree, but it's long enough to describe as a chain rattle. It would have to settle a lot, and something would be really hosed up. Speaking out of turn (because I can't name them at the moment,) there are some emissions devices that make odd noises even after the truck is off. Have you considered calling your local priest and checking on exorcism prices?

 

Bill, I haven't called the priest yet but that may be on the agenda soon.

 

Beau, after thinking some more, it did happen once while moving. Was at a gas station & it made the noise while I was filling up & then again just as I started to pull away from the pump.

 

Could possibly be emissions related. That stuff makes a lot of noise and especially when they get older. Trapped fuel vapor possibly? How old are your cooling components? How old is the thermostat? I've heard mine make strange noises as it cools down before. Did a timing belt job and the noise never came back.

I then put a flowmaster 40 series on and I don't hear much any more. lol

 

Exhaust heat shield rattle?

 

Don't think it's emission stuff. I have heard the VSV noise & this ain't it. Much louder & definitely metallic. Cooling system might be due for a flush/fill, I would have to check my records. Thermostat was replaced with last timing belt change. Not cooling down when it has sat overnight.

 

Not likely when the truck is not running & not moving.

 

wow I missed that in the first post.

so the truck is just sitting there, not running, and it suddenly/randomly makes a mechanical grinding noise similar to a spring unloading from being under tension?

Good lord. Sorry, I got nothing.

 

Does the noise always happen in pairs? It makes the noise then some minutes later it happens again?

 

No. When this first started, maybe 2 years ago, it only happened in single instances. In the last month or so it has happened both in pairs and single.