I searched through the forums but couldn't find any mention of the noise I've been hearing. When I'm sitting in the cab and the truck is idling, I hear a rattling noise. It's difficult to pinpoint the exact location, but it generally sounds like it's coming from the engine block itself or right under me. The noise is too faint to be noticed when I have the radio loud or am actually moving, but the noise is audible at idle whether the truck is warm or cold.

The noise itself is kind of hard to describe, but it sounds like an internal part rattling inside the engine, kind of a low vibration. It's not rythmic at all and there doesn't seem to be any consistency in how often it "rattles," except that it's always there at idle. It's probably worth mentioning that I can't hear it at all when I'm outside the truck or looking under the hood. However, I can feel the noise if I'm touching the intake or touching the exhaust near the manifolds.

It's gotten more noticeable since I bought the truck a few months ago. It doesn't seem to be causing any problems, but the noise is really starting to drive me nuts. You guys have always been pretty helpful in diagnosing problems - anyone got any ideas? Much appreciated!

'99 4.2 V6 2wd

 

I would check the cats first. When the ceramic breaks up inside, this can create a rattle. Also check the heat shield around the cats. Hope this helps.
Pasta

 

This was kind of a churping noise , it was irritaing enough to fix - I have a pic from the TSB and from my truck after the fix - click on the links


https://www.f150online.com/galleries...140&anum=10943

https://www.f150online.com/galleries...139&anum=10943

There's more heatshields under there , there easy to find , might wanna see if they worked loose as well.

Good Luck

 

I will try putting those bands around the cats - I stuck my ear right up to them, and though i couldn't tell for sure, I don't *think* that's where it's coming from. But I have heard that is a problem for my model year. Thanks for the tip!

 

Well, I tried banding up the cats, and the noise is still there. I'm starting to wonder if this could possibly be the alternator making the noise. The alternator's been making a knocking noise ever since I got the truck. Anybody think it's possible that the alternator could also be the source of the more inconsistent rattling noise I've been hearing?

 

[QUOTE=rumdrums]Well, I tried banding up the cats, and the noise is still there. I'm starting to wonder if this could possibly be the alternator making the noise. The alternator's been making a knocking noise ever since I got the truck. Anybody think it's possible that the alternator could also be the source of the more inconsistent rattling noise I've been hearing?[/QUOTE


Pull your serpentine belt off then start it - see if the noise is still present without the belt. If your alternator is the culprit this is one way to pinpoint it.

 

Just a suggestion but check the jack under the rear seat. A few weeks after I bought my truck I keep hearing a rattle or chirping noise from some where and couldn’t track it down, it was real faint and I couldn’t tell where it was coming from (it sounded almost like it was coming from the center consol) but after a few weeks of it driving me crazy I tracked it down to the jack. I just shifted everything around a little bit and it fixed the noise havent heard it since! But good luck with your hunt!