Today when I was out for a drive I noticed a rattling sound at idle. Couldn't pinpoint it under the hood. From inside the car it was quiet enough to get lost in road and engine noise. Car ran fine and made it home.

I went back out to go get some dinner a few hours later and the sound hadn't gone away, in fact it almost seemed louder. I took a video of it.


To me it doesn't sound as "sharp" as rod knock, plus blends into the sound of the engine above idle. Looked up piston slap but it doesn't go away when the engine is warm. Suspected timing chain but it actually gets quieter at that end of the engine - otherwise seems pretty uniform throughout the engine bay, and removing the NVH cover (or what little there is of it) makes no perceptible difference. No metal in the oil when I changed it, no metal on the (impossible to read) dipstick when I checked it after getting home.

It sounds similar to but louder than a noise I've been hearing for a while, but that noise would go away with a little touch on the clutch pedal whereas this doesn't respond to the clutch at all.

Car still felt like it had normal power, but also still shifted fine.

What is going on here?

 

Check whether removal of the accessory belt eliminates the noise.

 

Might sound like a stupid question but wouldn't removing the belt turn off the oil pump?

 

Good question

The crankshaft pulley rotates the accessory belt, and the crankshaft separately rotates the oil pump via the oil pump chain.

Therefore, removing the accessory belt won't affect the oil pump.

Removing the accessory belt will affect the water pump, but the test for the absence of noise is brief.

 

Have you checked the oil? If its not low on oil, and its not the timing chain it may be the friction wheel hopping.

 

It's not low, if anything it's a little high. Will let a little out today while I'm checking the belt and see if there's metal or plastic in it.

I hope it's the tensioner, would be a much cheaper fix than the clutch or flywheel let alone an entire engine

And now it's raining and I don't have a garage. Hope it stops before dark.

 

Could be a bad motor mount. You might try seeing how much engine movement you get engaging 1st and reverse (parking brake on, just slipping the clutch until the engine starts to lug).

 

So, update.

I wasn't able to perform the belt removal test today, but my handyman neighbor came over to look at the roof, I mentioned my car was making a bad noise, and he insisted on taking a look and a listen.

He found a rusty, wobbling idler pulley.

Would that cause this sound or did we just find an extra problem?

(At this point I'm convinced it's pure Divine intervention that it didn't break in use)

 

By idler pulley, do you mean friction wheel? If so, a damaged friction wheel is a common cause of engine noise, as mentioned by Raymo2u.

Diagram from Pelican parts.

 

It looked more like the gray arrow (AC compressor pulley) in your drawing, let me go look again real quick

 

Did you try turning on and off your AC? IT could be the compressors clutch that may need replacing. I dont think Ive ever heard an AC make a rattling noise, they usually scream or chirp.
If the entire pulley is wobbling, Id replace the compressor altogether...which is not fun, unless you dont care about AC. The lines have to be drained, compressor replaced, lines vacuumed out, and then refrigerant filled. This is not a cheap job if a shop does it. It is cheaper if you swap the compressor yourself and then have the shop vacuum and refill. I wont tell you to drain the refrigerant yourself, it is very toxic. (hold your breath around it if you do it).

I would still replace the friction pulley while you are in there, its good preventative maintenance that you will end up doing at some point. Make sure to get a good name brand as the cheaper ones off ebay fail quickly, same with water pumps.

 

So I went out and ran it again just to check. I think the pulley we saw was indeed the AC compressor pulley, however I didn't see it wobble this time. It did look to me like the serpentine belt itself was very loose and wobbly though.

I didn't really think about the compressor clutches because I hardly ever use AC, but the few times I did use it this summer (usually idling in a drive-thru) I seem to recall that it felt and sounded, on startup, like it hadn't been used in forever

 

A compressor pulley that makes noise even with the AC turned off would point to a failed AC compressor pulley bearing.
Remove the accessory belt to check whether the AC pulley wobbles when turned by hand. Also inspect the accessory belt, water pump pulley, friction wheel, alternator pulley, and belt tensioner.

 

If I were to do an AC delete would that knock out the heater as well or just AC itself

 

Just A/C if you only remove the compressor.

 

Good to know. Looked again and on second check I don't think I was actually seeing the AC pulley as only the idler and crankshaft pulley are really visible from the top down. Idler is suspect.

 

What do you mean by idler pulley? Friction wheel? Belt tensioner?

 

At this point, both. Even with a flashlight it's hard to see anything but judging by the shadow on the belt, the belt was flapping up and down, the tensioner wheel was shaking back and forth, or both.

Update: prodded around from above with a long thin stick. Everything seems pretty locked in place. Found and managed to push on the AC compressor pulley, it rotated without any clacking or wobbling that I could tell (albeit admittedly slowly and inconsistently due to the method used), however it was slipping against the belt as it did so, producing no movement elsewhere.

 

To identify the specific issue(s), raise front end on stands and then remove the right front wheel and the wheel liner. With the engine running, carefully observe the accessory belt and relevant components. Once the prime suspect(s) is identified, remove the accessory belt to verify that the noise is eliminated and then replace the damaged part(s).

 

Couldn't get jack stands under it because no one makes any smaller than 2 ton, couldn't get the fender liner off because the two T30 screws have the softest heads I've ever seen and cam out immediately if you try to turn them when they're stuck. Was able to get a partial video I'll have to post later.

Crankshaft pulley looked a little eccentric, friction wheel was definitely vibrating in use but it's hard to see in the video. Couldn't see the AC pulley while running but once I turned the car off, I realized I could reach it. With the belt in place it could spin by hand, very freely but not entirely silently as it produced some clacks and clunks while doing so.

At this point it's going to have to go to a shop so they can see if I need a new crankshaft pulley, a new friction wheel, an AC delete or all three

 

Good luck!

 

Im going to put money on the Friction Wheel and Tensioner, Id replace the belt also. I just replaced these myself, the tensioner was failing, causing the belt to hang halfway off the tensioner, causing issues with alignment - making noise.
You can get everything in one place HERE, and its made by Dayco (OEM Quality).

 

The loose belt is definitely consistent with a bad belt tensioner.

 

So, a little bit of an update. Took it to a local import shop, they checked it out. Know what was actually making that noise?

A rock. There was a rock stuck in a crankshaft pulley groove, rattling around, making that noise. I live on a gravel road and probably picked it up doing a parking brake slide.

It'll probably need belt system maintenance soon anyway, but man that's... actually a relief, knowing I don't need a $250 part from out of state or a whole new engine. Thank God it turned out to be something so trivial!