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1999 323i
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Discussion Starter #1 (Edited)
Hello! New to the forum! Picked up a 1999 323i last night as a project, and I'm already here! (No complaints, I've been dying to get under a hood again!)

I've scoured the internet all over for this particular sound I'm hearing and I CANNOT figure it out. The best way I could describe the sound is somebody hitting the bottom of a bucket once every few seconds while my engine is running. It's not a repeated knock or tick, it's more like a thump.

I can only test it at idle in the driveway because it's not registered yet. Didn't seem to make the sound while I was on the freeway driving it back to my house. Just noticed it this morning.

If my online sleuthing skills have diminished and this has indeed been covered in another thread, please link it.

Thanks in advance

1999 BMW 323i, m54tub25 m52tub25
Sorry, I accidentally typed a "4" instead of a "2". Should probably proofread better.
 

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1999 323i
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Discussion Starter #3
Engine mount?
[/QUOTE
Not likely. It's doing it at idle, and the engine doesn't "roll" or "flex" like one does with a bad engine mount.

When I said it sounded akin to somebody hitting the bottom of a (plastic) bucket, I'm pretty close to the exact sound. Very random. Every 5-20 seconds give or take
 

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E30M3 Race F10 535 R1150Rt M Coupe
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4,041 Posts
Need a video, as much as I hate those.
Intermittent misfire?
 

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Water pump starting to fail and hitting the insides?
Use a mech's stethoscope or a long stiff hose like flexible electrical conduit to isolate the source. Maybe the tensioner on the belt? Not sure I've heard of oil pumps thumping...but some models had issues.

Disa flap?

Isolate the sound...or you'll get a million guesses that are wrong like mine. :)

Read codes if you haven't.
 

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Right? Anything that builds/loses some kind of pressure. Inconsistent bumps. These M54’s are really quiet, so it’s easy to know when something is off, especially at idle. My southern South Carolina instinct says “just drive the piss out of it and wait til it breaks.” It either will or won’t. Hell, just a low oil level makes the valve lifters noisy, and we all know how easily that comes with the high mile M54.

Kind of makes me think “do all the common maintenance/prevent Mantenance” and see if it goes away. If not, just drive the car and wait. We all know pulleys/tensioner/CCV/Alt/A.C./water pump/Vac/DISA/ICV can all make thumps.
 

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1999 323i
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Discussion Starter #11
Sorry for the belated reply. I've been busy all day. I decided to take a video of it to better explain.

For the record:
That intake was not my doing. That was on there when I bought it.
 

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1999 323i
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Discussion Starter #13
Water pump starting to fail and hitting the insides?
Use a mech's stethoscope or a long stiff hose like flexible electrical conduit to isolate the source. Maybe the tensioner on the belt? Not sure I've heard of oil pumps thumping...but some models had issues.

Disa flap?

Isolate the sound...or you'll get a million guesses that are wrong like mine. :)

Read codes if you haven't.
Codes are p0150, p1189, and p1188
p0150 is B2S2 o2 sensor, I know that much off the top of my noggin. The other two, I'm unsure of.

I'll try the stethoscope!
 

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1999 323i
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Discussion Starter #14
Right? Anything that builds/loses some kind of pressure. Inconsistent bumps. These M54’s are really quiet, so it’s easy to know when something is off, especially at idle. My southern South Carolina instinct says “just drive the piss out of it and wait til it breaks.” It either will or won’t. Hell, just a low oil level makes the valve lifters noisy, and we all know how easily that comes with the high mile M54.

Kind of makes me think “do all the common maintenance/prevent Mantenance” and see if it goes away. If not, just drive the car and wait. We all know pulleys/tensioner/CCV/Alt/A.C./water pump/Vac/DISA/ICV can all make thumps.
It's an m52, if it matters. Didn't mean to type "m54". I'm a wee bit dumb 😂
A quick tune up and fresh fluids is happening soon.
 

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2004 325i automagic
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3,028 Posts
Isolate the sound...or you'll get a million guesses that are wrong like mine. :)

Read codes if you haven't.
OP, do both of the above. Wish you hadn't shut off the engine before going around to the engine in the video.

Like dmax suggested, use a long hose or even a long screwdriver as a stethoscope to locate where sound is or even isn't coming from. Get front of car in the air and poke around underneath also. Just be careful around spinning objects at the front.

You can also remove the accessory belts one at a time and run the engine to see if anything run by them are the cause, but don't run it too long without the big serpentine belt that drives waterpump, otherwise it will overheat.
 

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1999 323i
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Discussion Starter #17
OP, do both of the above. Wish you hadn't shut off the engine before going around to the engine in the video.

Like dmax suggested, use a long hose or even a long screwdriver as a stethoscope to locate where sound is or even isn't coming from. Get front of car in the air and poke around underneath also. Just be careful around spinning objects at the front.

You can also remove the accessory belts one at a time and run the engine to see if anything run by them are the cause, but don't run it too long without the big serpentine belt that drives waterpump, otherwise it will overheat.
Cool. I'll start running without belts. If it continues: stethoscope time. I'll report back with my findings (likely tomorrow)
Thank you all
 

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Make a video under the hood. We neec to narrow down the area.
Have you checked the oil?
You can google those codes. Did you get with check engine light on? And DSC?
 

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You're sure you don't have a live catfish flopping around in there?

If the noise unchanged after removing the belt, then I would remove the idler control valve ICV and see if the spinning valve is jammed.

Also the CCV (oil separator) vacuum regulator diaphragm stuck and jump could cause this noise. You could use a clear hose to have a water column and have one end insert into the dipstick tightly and use it to monitor if the crankcase pressure jumps whenever that noise happens. The water column movement indicates the pressure jumpy or not.
 

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Before you start taking the car apart, we need to get more info on the general area under the hood. And the oil level.
Try the belt test.
 
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