I was foolin around under the hood the other day and noticed that whenever I revved the engine up a bit and then let off, you could hear a rattling type noise coming from inside the engine. Seems to happen the most around 3K rpms as the engine is spinning down, it's been freaking me out ever since, I can't figure out what it might be. Any ideas?

 

is it more like a "squeeking" sound?

 

No, definitly sounds like rattling, it's faint and easy to miss if you're not listening for it.

 

mine does the same thing.

 

is it really loud? Could be loose exhaust OR you could have a blown exhaust gasket like I did racing a honda the other day

 

apex seal chatter?
Who knows, sounds are so hard to diagnose when you can't here them.

 

check your accessories...my power steering pump rattled when it died.

john

 

Check your air return line from your cat. Mine used to like to vibrate against the exhaust shielding at idle (drove me nuts.) Check the damn shield above the exhaust header, too. Might be loose.

 

I have no accessories to speak of really (no AC or PS), and I have no cats or header shield either. Apex chatter crossed my mind, but I have no clue what it sounds like, how loud it is, when it happens, etc. I pulled my MOP about a month ago and been premixing 16oz. per full tank fillup... is this possibly related? How many other people have this rattling?

 

I have this sound too, and I think it's the heat shield on the exhaust manifold. I haven't put too much thought into it yet tho.

 

Its the squirl getting tired-tripping and bouncing around in there. don't worry it gets back up.

 

Are the exhaust sleeves in the rotor housings present? I've heard of those sleeves coming loose, and rattling at a certain RPM. It's rare, but it's been known to happen...

 

Bearings will rattle when they go out. Easy to check, just need a stethascope. Automotive ones aren't too expensive but if you have a medical one laying around you can use that too. Toutch it to the alternator, water pump and air pump(if you still have that) and see if the sound is comming from any of them. If so you'll know it. If it's in your engine(God forbid) good luck.

 

It better not be the bearings, engine only has about 5k miles on it. I think you're right about the sleeves Zach, my front rotor sleeve was loose when I installed my header awhile back. I didn't even remember that till I read you're post, that has to be what I'm hearing.