New noise from engine
 

What is that sound? It comes from the engine, follows the engine RPM, comes and goes randomly. It started yesterday after an hour of smooth driving and would go away if I put it in neutral and let it get down to idle. This morning in the cold it did made the noise a lot until it warmed up. It sounds a little rougher in person, but not quite like a plastic gear grinding. Stereo is off and it's definitely not coming from the speakers.

Shorter video where it was recorded better:
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Longer video where you can hear the way it follows engine RPM:
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Idler bearing
Power steering fluid
Belt tension

Get a mechanics stethoscope (metal tip) and see if you can isolate the sound.

Careful not to stick it in something moving.

regards
Gary

Good idea. I'll see if it will make the noise while parked. If so I should be able to find it with the mechanic's stethoscope (I have a decent one).

Yeah, my serpentine belt will make a similar noise (although much quieter) when its really cold outside until it warms up. The belt, tensioner, & idler pulley were replaced at the 150,000 mile service, so they're not that old.

Now that you mention it, forever I've had a noise that I attributed to the serpentine belt that happens shortly after starting in the cold, but I've never been able to hear it inside and I don't think it continued while driving...just while idling. It is vaguely similar.

I'd love if it turns out to be the belt and/or idler and/or tensioner.

That is a pretty high pitch whine from 1000 - 2000 rpm of engine speed so I would say it would have to be the alternator since everything else turns at a much lower RPM. Something that loud could be the transmission too but more likely the alternator bearings or cooling fan on the alternator. Check for red dust and oil stains on the alternator as well as black belt dust.

I assume you don't have a Supercharger or Turbo in that engine?

Definitely not transmission. It stays with engine RPM even in neutral.

No forced induction.

That's two votes for alternator (one on another forum). I'll be so happy if it turns out to be something easy and inexpensive like all these suggestions.

So that's where my vacuum cleaner went. :)

Spray some brake cleaner on the belt and see if it goes away.

regards
Gary

Yeah, I first thought it sounded like turbo whine too, but knowing that he didn't have a turbo I immediately dismissed it.

hmm yes all good suggestions so far.

ive heard powersteering pumps make weird noises especially when it sucks up a bubble (low fluid)

could be belt, could be alternater

somehting else it could be since you say it does it and goes away with temps is a vacuum leak, partially cracked hose can cause a whistle or a whine sometimes, or it could have popped off. this would be my best guess.

its obviously somehting engine driven or engine itself so just check anything that roatates

A leaky vacuum hose? I had a somewhat similar noise in the Geo, and it turned out to be a collapsed vacuum hose, vibrating.

yea sucks in air in small cracks causes a hell of a noise or can do what you said. kinda like the ol blade of grass between your thumbs:p

My wife described the sound exactly that way.

Make that three. I'm not guaranteeing, but as best I can tell with the poor quality recording and playback it sounds like an alternator.

And while we're at it, add one vote for forced induction. A supercharger on that would be fun. :)

-BC

CORRECTION: A supercharger on that would be a lot of fun.

something driven by the belt. Most likely the alternator.

I happened for a few more days but never dependably enough that I could stop and touch stuff with the mechanic's stethoscope while it was still happening. It hasn't happened at all in a few days.

I guess I'll have to wait for it to return and get worse before I can diagnose it.

The vibrating vacuum hose problem I had came and went in a similar fashion...

It is the alternator with the bearing running out of lubrication it will make noise when the belt is cold and tighter putting more load on the bearing and once it warms up the lube will move around and quiet it down and the belt will stretch a little. The Alternator is the only belt driven device that is geared up to a higher RPM while everything else is slower or about the same speed as the crank. Check for dust around the bearings as well as any play in the shaft of the alternator then you can loosen the belt and try spinning the alternator by hand and see if it feels a little bumpy - that will tell you right away.

A far stretch would be the starter motor gear not returning from the flywheel.

That sounds logical to me. I can check that without waiting for the noise to return, too.

If it's the alternator I can totally ignore it until it fails to produce electricity...right? Granted, that day will suck.

well typically when the alt fails especially bearing wise it locks it up thus dystroying the belt.

if it comes and goes id say you have some time left but id be weary of driving it super far from home

Running an alternator till it fails to produce electricity is usually a voltage regulator failure. Voltage regulators generally don't make any perceptable sound, but if you have problems your voltage will fluctuate, and one day it just won't work.

Hmm...if it locks up, that's not so great.

Perhaps I'll just wait until next month and see if I can scrape up the money for a new alternator by then, assuming that I positively diagnose it as the alternator.

Check it and if it is the bearing just change the bearing. They should be standard sealed bearings.

I didn't know alternators were that easily serviceable. Cool.

Yes, alternators are serviceable, and you can get bearings and even new voltage regulators for them, but if all you want is a stock alternator you can usually get a rebuilt stock GM alternator with a lifetime warranty for $50. I did splurge when I put a new alternator in The Beast - When the original alternator gave out I put an upgraded 165 amp alternator in. The Buick and Rusty are both running 105 amp alternators when they came stock with 70 amp alternators. I always believe in oversizing the alternator.

Where could I get a rebuilt unit for $50?

Mine is already an upgraded capacity unit for my towing package, and it's way more than I ever need even when using four electric brakes heavily on my camper...

When an alternator bearing fails, it can be rather spectacular...been there, done that.

If you're running an oversized alternator you won't get a $50 one. The last alternators I bought were oversized, but still stock alternators in my Buick and in my 86 Chevy. I think those ran me like $70/ea and came with a lifetime warranty. I think I bought them at the local NAPA dealer. I could have had the original 70 amp alternator for about $50. The alternator in my 98 GMC is a custom aftermarket alternator, 165 amp. If I remember correctly stock is 120 amp. I oversized the alternator because its nice to be able to jump start anything, and I was thinking about installing an AC inverter on the truck at the time.

I was looking online (I assume this is the Rabbit, right?) and saw used alternators for about $85. I was surprised to find that Autozone.com didn't list a rebuilt alternator for that car (maybe not that many have broken yet?)

This is for the GMC. If it was the VW, that's under warranty.

I checked Advance Auto and they were $150-300. Looks like that's the going rate everywhere.

The price must have really gone up in the last 2 years since I bought one, or your truck uses a less common style. The alternator in my Buick and my 86 Chevy is the same one they put in most vehicles for probably 30 years, very common, very cheap. The one in my 98 GMC is the same style that they used in the late 80's through the 90's. I don't know if they switched styles of alternators when the vehicle was redesigned though.

RockAuto.com...starting at $107.99 for either 105 or 130 amp alternator. I'd probably try the local junkyard first...

RockAuto seems to have the best prices I've seen for my Cad's parts so far...and shipping was pretty quick.

https://smiliesftw.com/x/picard1.gif Why didn't I check rockauto?

or take the alternater off and take it to autozone and they test it free...find out if thats truley the issue before dumping $130+

I definitely won't buy a new one until I'm sure of the diagnosis. Thank you for reminding me of free alternator testing.