Random sqwawk noise - 2011 Holden RC Colorado

Question

As title - I can only describe it as a sqwawk noise, like a disk that vibrates side to side at a resonant frequency. It's been in my car for a significant amount of time and nothing I've done has fixed it.

At first, I was pretty certain it was an idler pulley due to the bearings on it being wobbly, so I replaced it. No luck.

I thought it may have been the alternator. I haven't replaced it, but it looks to be in perfect condition. The belt is running perfectly straight and there's no side play in the armature. I've had no charging issues, and my idle RPM hasn't changed at all.

AC? Maybe - though the sound never happens in neutral even when the AC is running, and turning off the AC amidst the sound doesn't always stop it.

I'm worried it could be something in the transmission, because the sound only happens when it's in gear, but I also feel it might not be something in the transmission, because no matter what gear, what speed and what RPM, it sounds exactly the same. It's not constant either.

It'll happen once the car warms up a bit - usually 10 to 15 minutes most commonly, though it's not unheard of for it to happen immediately; it'll only sound for a few seconds, and I'll then take my foot off the accelerator and 8 times out of 10, it'll stop and be a normal car until the sound is triggered again. I'd estimate that it sounds 10 times every 15 minutes during slower driving.

I can't hear it at high speed, mainly only first, second and third gear.

I have only heard it up to 50kmh.

Absolutely no performance decrease noticeable.

I can feel the vibration in the gear stick, but the sound (especially with the windows down) is really loud from the engine bay.

It's the biggest pain in the ass, because there isn't one symptom that is constant - and I haven't found any sound on the internet that is the same.

I'm at the point I wish it would just break, because it's really embarrassing when driving through carparks and places where there's people. It's been 2 years. The sound is exactly the same, the frequency of it occurring is exactly the same, literally everything is the same. It's as if someone has put a Bluetooth speaker under the hood to take the piss.

I can upload the sound if you guys would like. For now though, imagine the sound of a rough metal plate spinning around on a marble bench super fast until it lays flat, mixed with the sound of a little grinding at the same frequency. It's not high pitched.

Answer 1

Hearing the sound may help -- this is definitely a perplexing issue.

It sounds like you have ruled out a slipping belt, alternator, and potentially A/C noise. It does sound like A/C to me when the A/C clutch engages, but if you have A/C off and you don't have defrost selected (some cars turn on the A/C if you turn on the defrost), then you have probably ruled that out.

If this is a manual transmission, then it is possible that the throw-out bearing is causing the noise -- try pushing in the clutch when you hear the noise. Another cause could be a bushing in the transmission that causes a shaft to resonate. This could be temperature related and it is a very distinctive sound that is hard (for me) to describe.