Alternator whine, videos attached.

Meds

Meds

Active member
 Beds/Cambs
Hi guys..
Ive had an annoying electrical type whine for a long while, not enough to cause concern but enough to annoy.
It's like car is supercharged.

This week I dropped in at my local mechanic, he came out for a road test and heard it. We got back to workshop and a stethoscope confirmed the alternator is whining away with a lovely 'weeeeeeeeee' sound..

OK, no problem, easy.
New alternator ordered and I fitted it myself yesterday.

The new one is pretty much making the exact same 'weeeeeeeee' supercharger sound when driving. Using a screwdriver pressed onto the housing and my ear confirms the new alternator sounds just like the old one.
Audible while driving, just like the part I replaced.
Not a bearing grumble sound an electrical type sound.

Have I been unlucky to get another alternator with the same annoyance.? Original part was BMW Bosch, new part is Bosch.

Belt, pulley and tensioner already replaced a short while ago.

Ideas?

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[Edit/update:] I'm honestly starting think this noise is absolutely normal, 2 people have now told me their N52 sounds the same, I've found numerous videos online from people trying to identify other noises and I can hear that faint whine in the background then they rev the N52 up to 3k rpm and then decelerate.
The stethescope does indeed amplify a whine sound (as designed)
That combined with with me wrongly comparing the noise to my previous 2 N52 130i's (with probably MUCH more sound deadening than the Z4) sent me down a wrong path thinking there was a problem, when there is not.
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Did it do it before you replaced the other parts?
Just wondering if you have a tensioner that is holding it too tight?
 
Alternator was replaced after the tensioner.. the noise was there before the tensioner swap, too.

I have considered the theory of the belt just being too tight but as the tensioner has been swapped, not because it was faulty, just as a sevice item when I replaced the belt a while back.

I'm perplexed.
 
Is it definitely the alternator? Have you ran the engine without the belt just to verify that the noise is definitely belt related?
 
Regarding the 'without belt' idea. That was my next Q.
I can do that safely without any problems?
I assume power steering, AC and obviously alternator will stop functioning.
But I can test with it revving on my drive, I dont need to drive it, so should be fine..
 
Just start it, no need to rev it. Won't cause any problems and you will know within seconds if it is a belt related problem.
 
Meds said:
Regarding the 'without belt' idea. That was my next Q.
I can do that safely without any problems?
I assume power steering, AC and obviously alternator will stop functioning.
But I can test with it revving on my drive, I dont need to drive it, so should be fine..
Click to expand...
Unless you've modified it, the power steering is electric.
But yes, you can run it long enough to see if the noise goes.
 
Oh yes of course.. EPAS, not hydraulic. :rofl:
If i get a chance later, I'll drop the belt and see.
 
OK the plot thickens.
Dropped the belt, alternator much quieter when listening with a screw driver.
Put belt back on, still much quieter.
There's noise there but not as loud as the original or the new one when I tested yesterday.
How odd.

EDIT: I was imagining things, on a road test, noise is still there. Seems like listening while idle is not a good method to produce the noise.
 
Hi, might be barking up the wrong tree but I’ve heard that a similar whine noise can occur when the oil filter is not clicked in place in the housing.
Have you changed the oil recently? Easy to lift the oil filter housing cap to check (assuming you can find the 16 sided oil filter housing cap tool and don’t need to order another one like I usually have to…).
 
Yes, that's a good comment. Oil filter is fine, though, I swapped it out only the other week, just because.. :rofl:

The noise is still there i was imagining it had gone.
I took 2 videos to try and demonstrate the noise.
The 1st is just slowly engine braking around 2.5k revs, 2nd is slowly driving around the same revs, harder to hear on the 2nd.

https://youtu.be/r_SzqiHnNXU?si=VSg0Ee3BVOkc35zR

https://youtube.com/shorts/pFV9A6Xohi4?si=vuJwK2yOKVnSpN5f

Thos noise is not intrusive at all when 'on it' , just when slowly driving around when the engine is not under much load the zorst is quiet and road noise low.
 
Meds said:
OK the plot thickens.
Dropped the belt, alternator much quieter when listening with a screw driver.
Put belt back on, still much quieter.
There's noise there but not as loud as the original or the new one when I tested yesterday.
How odd.

EDIT: I was imagining things, on a road test, noise is still there. Seems like listening while idle is not a good method to produce the noise.
Click to expand...
If you removed the belt the alternator wouldn't be moving, so why were you listening with a screwdriver? Did the noise dissappear when you removed it?
 
Listening to see if something else was resonating via/through the alternator from around it maybe. But obviously yes, it wasn't spinning, so no noise from it directly.

I've got a helping hand tmrw, so I'll get some revs into the engine and get a good listen while my helper is on the peddle.. It's most prominent between 2.5 and 3k rpm.

How long do I have before the battery dies if I take it for a road test. ?
 
Meds said:
Listening to see if something else was resonating via/through the alternator from around it maybe. But obviously yes, it wasn't spinning, so no noise from it directly.

I've got a helping hand tmrw, so I'll get some revs into the engine and get a good listen while my helper is on the peddle.. It's most prominent between 2.5 and 3k rpm.

How long do I have before the battery dies if I take it for a road test. ?
Click to expand...
That is definitely the way to go. You need to rule out if it engine related or belt related. How long will the battery last, no idea but hopefully you will not need to drive it. Just out of curiosity, when did the noise first appear?
 
The new Bosch came with the clutch pulley already installed. :thumbsup:

I should know more tmrw, after a few tests.

It's been making the noise for 18 months, since i've owned it, and is only really there if you listen for it and the car is in the zone where it's above all the other noises.
Otherwise, the car runs superb, just as sweet as my 2 previous N52s.
 
When my alternator failed without me knowing I managed to drive over 20 miles on just the battery before everything electrical died I know this because my hardwired dashcam didn't come on on startup.

I assume on the n52 engine you would still have a working water pump on battery alone I wouldn't want to drive far just in case tho
 
I performed some tests this weekend. I was able to run the car with and without the belt.
There's no real difference when idling or revving on the drive between the 2.5 and 3k rpm range, and doesnt sound bad at all. Just the normal whirring from the 100's of parts moving inside the engine.
My helper says I'm imagining it, it sounds perfectly normal to him.

This doesnt explain the stethoscope test with my mechanic (I only have a basic screwdriver method), but again, maybe that's just perfectly normal and there's no problem, a stethoscope will amplify the normal noise, obviously.

I've got videos from both belt on and belt off.

No belt:
https://youtube.com/shorts/dV3-8h1Irdg?feature=share

Belt:
https://youtube.com/shorts/NLjJ5z-OcNg?feature=share

They both sound perfectly normal to me. :rofl:
 
I'm honestly starting think this noise is absolutely normal, 2 people have now told me their N52 sounds the same, backed up with a phone call and video from another, I've found numerous videos online from people trying to identify other noises and I can hear that faint whine in the background then they rev the N52 up to 3k rpm and then decelerate.
The stethescope does indeed amplify a whine sound (as designed)
That combined with with me wrongly comparing the noise to my previous 2 N52 130i's (with probably MUCH more sound deadening than the Z4) sent me down a wrong path thinking there was a problem, when there is not.
 
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