M42: Whistling noises FFT FFT like a stage3 supercharger causing stage4 depression

[s-thetikz]

searching for appropriate onomatopoeias is pretty much the bane of all car problem research, so i apologize for anybody in the future searching for this.

my m42 has been doing this for quite some time now, perhaps after an oil change? i also used mann oil filter, which i've heard isn't good, but i also purchased a stethescope and it has not given me any more clues as to why this is going on.

the sound: completely RPM dependent, gets louder with higher RPMS, somewhat quiet at idle. but gets suuuper loud at speed. i took belts off (both accessory and PS belt) and the sound stopped? maybe i should take it around the block, i've only done it stationary. tried taking off just PS belt and still made the same sound.
Heres video:
https://www.youtube.com/watch?v=dwS7...b_channel=EugK
^ why can't i embed?
pulls quite strong, temps are good, just that noisy ass chugga chugga chugga fft fft fft noise. sounds like a whistle almost at higher speed. tried soaping belt, same sound.

idle can sometimes stick around 900~ but settles at the 9:00 position (around 600-650).
voltage fluctuates at 14.1 ~ 13.9 and drops with accessory usage.

before sound:
oil change
VCG

i will note what i've done recently after the noise began:

water pump / thermostat
belts
chain tensioner (this might have been around the same time?) i did stethescope this and a sound emitted with a similar cadence but not definitive

i have a taped up intake elbow that i have been meaning to replace, but i doubt that such a noise can come from that, right? it's not like the seal is that bad.


i think that's about it in terms of info. really hope you guys can help me crack the case!
pic of said piece of shit:

[jbontke]

Check the alternator with a stethoscope. My alternator was loosing a bearing and it sounded like a supercharger.

[s-thetikz]

Check the alternator with a stethoscope. My alternator was loosing a bearing and it sounded like a supercharger.

i did check it, what sound did you hear? there's no irregular or pulsating noise coming from it that seemed unusual... i couldn't put it on the spinny part so i just placed it against the housing but can't hear much. i did free spin it before and it sounded... fine? so i don't know

[jbontke]

It would be very loud compared to the rest of the engine block. I cant remember the exact sound with a stethoscope, just that it hurt my ears compared to the rest of the engine. When i pulled the belt off, it had lateral play in the pulley.

[onesecond]

Personally it sounds like something rubbing against some plastic or a belt. See if maybe a leaf or the insulation from the hood fell in somewhere?

[s-thetikz]

It would be very loud compared to the rest of the engine block. I cant remember the exact sound with a stethoscope, just that it hurt my ears compared to the rest of the engine. When i pulled the belt off, it had lateral play in the pulley.

i'll check again for play... was your noise a constant whine or did it have a chugga chugga to it?

[82eye]

sounds like a bad alt to me. alt, ps pump, or air con pump, it's something on a belt for sure. alts are almost always the first to fail. you'll know for sure if it progresses to charging issues.

[s-thetikz]

sounds like a bad alt to me. alt, ps pump, or air con pump, it's something on a belt for sure. alts are almost always the first to fail. you'll know for sure if it progresses to charging issues.

i took off the PS belt and the sound remained... the pulley on the PS pump had about 1cm of front and back play.

i'm going to pull the tensioner to see if it's binding at all, but the sound was there before the tensioner was replaced so i have my doubts

[s-thetikz]

update: took off PS belt, still chugging away, valve train noise almost drowns out my incredibly loud muffler at higher RPM. timing chain? :(

still haven’t pulled tensioner, will do that tonight.

[82eye]

update: took off PS belt, still chugging away, valve train noise almost drowns out my incredibly loud muffler at higher RPM. timing chain? :(

still haven’t pulled tensioner, will do that tonight.

good call on the tensioner. that's a great bet.

edit : gorgeous car btw.

[s-thetikz]

thanks, hopefully i can get it sounding gorgeous too..

[s-thetikz]

update: so i tried spraying some wd40 on the front of the alternator, the sound stopped suddenly, then it came back to me with an unusual creaking noise.


this might just be the culprit! now debating whether to just buy a new alternator altogether or just the bearing. anyway, this bodes well for the repair, hopefully, and could also explain why my voltage would hang sometimes at 13.9 instead of a full 14.1

[bmwman91]

Wow, I am glad that it seems like you have a positive indicator of the issue now.

If the alternator is of unknown age, I vote for replacing or rebuilding it. I had mine rebuilt locally for about $120 and it was as good as new (new bearings, diodes, regulator, and they hot-tanked everything).

[s-thetikz]

Wow, I am glad that it seems like you have a positive indicator of the issue now.

If the alternator is of unknown age, I vote for replacing or rebuilding it. I had mine rebuilt locally for about $120 and it was as good as new (new bearings, diodes, regulator, and they hot-tanked everything).

i was just planning on replacing the bearing(s). should i bother doing this or just buying one second hand on ebay?

i suppose i can go to somewhere somwhat local and have them rebuild it as well

[bmwman91]

If you can find a local place that will rebuild it, check that out. New ones are (I assume) expensive, and putting a used one in is kind of a lot of work for something that might die in the near future. Then again, if it is otherwise working fine and you can source the bearings, it could be fun to DIY it.