What is this sound?? Please help!!

[StudioWizard]

My 2005 2.5i has been making a funny noise intermittently. It's most noticeable when the car starts moving in gear. It doesn't do it much if at all in idle or revving the engine, although I was able to make it occur if the car was stopped on an incline.

Here's a video link of it:

https://youtube.com/shorts/nEbDokKmh_s

I know what's NOT causing it because I had these items checked and/or fixed/replaced:

Belts, tensioners and pulleys (all were replaced)
Transmission / torque converter (trans was rebuilt and TC replaced)
Fuel injectors (all replaced)
Wheels / bearings (both ruled out by mechanic)

The only things that haven't been checked/replaced are the catalytic converter and alternator. Does anyone have any idea what this noise is?

[Z4Mariner]

While the possibilities are not endless, there are a lot, and diagnosing from afar is tough. I'm sure it's irritating !

Things to check: 1) Heat shields - check carefully for fasteners where the heat shield has corroded or worn a hole large enough to make the fastener loose. Or you may find a fastener missing. Look for any place the heat shields are close up against the chassis or each other, but still loose enough to move by hand - the heat shields can amplify the noise, and they may move and flex under acceleration. 2) Though it doesn't sound exactly rotational, other items have bearings that can go bad - did the shop check the water pump and AC compressor clutch assembly bearings while the belts were off ? 3) Loose or shifted exhast hangers might cause your exhaust to rub against heat shields or chassis only under certain throttle or road conditions.

Nothing I suggested is a sure thing to be your noise, but they're worth checking, and they could be done as DIY. They mostly take time.

[BumpyZ4]

Sounds like something flapping under the car like heatshields or even the plastic covers under each side of the car. I had something similar and found the plastic cover on the driver side (LHD) had several studs that hold the cover on had been ground of by scrapping curbs/speed bumps and the cover was flapping in the wind.

[StudioWizard]

...did the shop check the water pump and AC compressor clutch assembly bearings while the belts were off ? 3) Loose or shifted exhast hangers might cause your exhaust to rub against heat shields or chassis only under certain throttle or road conditions.

Yes, checked and replaced it.

I'll try to check the heat shields, etc.

I took the car out to a street with sharper incline and noticed the car will make the noise while idling in neutral. When I turn the car around on the same incline so the car is pointing downward, the sound mostly goes away during idle and even when I start drive off.

[StudioWizard]

Sounds like something flapping under the car like heatshields or even the plastic covers...

That would be great if that's what it is. I just spent $1,000 changing the belts, tensioners, pulleys and water pump. The mechanic and I were pretty sure that would solve it, plus the water pump was poor quality plastic one that a previous owner must have installed.

I hope to god it's not the cat converter.

[Dr. Zed]

It almost sounds like your lifters. It might explain why the noise sometimes goes away when on an incline since it might impact oil uptake which can help with lifter tick noises.

It's sort of hard to fully be sure obviously but it's definitely rhythmic which makes me believe it's mechanical in nature and not a piece of loose plastic.

Although, I'd be very shocked if it was that and the mechanic you brought it to didn't identify it because they definitely should...

[StudioWizard]

The mechanic has done a LOT of work on this car, so he definitely would've mentioned the lifters. I've spent a fair a mount of time with him and his primary mechanic trying to figure it out. We've put it on the rack several times and once we even put ran the car in gear on the rack while we inspected underneath. In that case, no weird sounds. So, the car needs to be on the ground or something. So then we did various road tests while somebody listened outside the car. They both say they've never heard anything like it before. It's killing me!!

I've put quite a bit of $$$ into getting this car into shape, so I'm fully invested now. haha

[patriot66]

Is the sound coming from the engine bay ? Have you checked the DISA valve ?

[StudioWizard]

It sounds like it's coming from the left underside of the car. If I stand on the right side while somebody does a drive by, I don't hear as much. The way I recorded the sound hear on the video was by putting my phone outside the (US) driver side window.

It's definitely NOT the DISA valve. I personally rebuilt that unit with the metal/aluminum upgrade kit. (I did a whole post about that. haha)

Good questions, though!

[patriot66]

It sounds like it's coming from the left underside of the car. If I stand on the right side while somebody does a drive by, I don't hear as much. The way I recorded the sound hear on the video was by putting my phone outside the (US) driver side window.

It's definitely NOT the DISA valve. I personally rebuilt that unit with the metal/aluminum upgrade kit. (I did a whole post about that. haha)

Good questions, though!

You should always double check. Items that are replaced or repaired CAN fail immediately or very soon after....sods law !
So, does the noise happen when the car is in drive and moving AND also at idle in drive with foot on brake ? Is it present with engine running and in park/neutral ?

[StudioWizard]

So, does the noise happen when the car is in drive and moving AND also at idle in drive with foot on brake ? Is it present with engine running and in park/neutral ?

The noise doesn't really happen unless the car is moving even if the car is in drive with the brake on. We tried that at my mechanic's shop a few days ago and it didn't do it. We also put it up on the rack and put it in gear so the wheels were spinning. It didn't do it then either.

I can make it happen a little bit in park/neutral if the car is pointing upwards on an incline and I increase the rpms. If I turn around and point the car downward on the same incline, it doesn't really do it. Same thing if I'm just driving.... it's more pronounced going up an incline and almost nothing going downhill. And sometimes it just goes away completely... maybe after driving a while, but then comes back. It's really weird.

[patriot66]

Sounds like the noise increases with engine speed to me. Timing chain/guide/tensioner ? Oil pump/chain ? A/C pump ? Is alternator OK and secure ?

[StudioWizard]

It only increases right when the car takes off. Otherwise, it's intermittent. At freeway speeds, I can't hear it because of road/wind noise, so not sure if it's doing it or not.

In the video, you'll notice that as soon as the car starts to move, the noise starts. What happens past the video is the noise starts to go away. It's the worst once the car starts to move, then it stabilizes and diminishes.

It almost sounds like something is scraping, doesn't it?

[StudioWizard]

Sounds like the noise increases with engine speed to me. Timing chain/guide/tensioner ? Oil pump/chain ? A/C pump ? Is alternator OK and secure ?

The alternator is doing it's own whining noise intermittently, so I'll have to change it. It's possible the alternator is also making this noise. All of the tensioners, pulleys, belts and water pump were just replaced. Spent $1000 and it didn't solve the problem, but at least I'm set on belts, pump, etc for the foreseeable future.

[patriot66]

Check brake disc shields and exhaust heatshields