Engine Squeal, Can't Pin Down Source - Corolland: the Toyota Corolla Forums

Thanks in advance for consideration. I've searched here and in the Googleplex, and nothing I've found matches my symptoms. 1996 Corolla, 1.8L, 5-speed manual, 223K miles, engine rebuilt at 190K, has been running great since rebuild, but an elusive squealing noise has been getting slowly worse over the last year or two.

The reason I haven't dealt with the noise is because, for a very long time, I assumed it was coming from the power steering pump. The pressure hose has had a slow, stable leak since before the rebuild, and since I had a tough time replacing it long before the rebuild, I've just monitored and refilled the reservoir when necessary. For quite some time, the noise was more like a quiet gurgle that only happened between 1800 and 2200 RPM under fairly strong acceleration. Now that the noise has become more frequent, higher-pitched and noticeable, I have ruled out the power steering system. I can't pinpoint the source of the noise, but it's definitely not the PSP.

Intermittent: Everything is normal at idle, and at any RPM when cold. After about five minutes of driving (regardless of the temp gauge position), the low-pitched squeal will happen when the engine is under load, and RPMs are around 1800-2500. No connection to steering input, speed, AC status, or anything but engine RPM. The squeal will not happen when revving the engine in neutral, unless it's been running for 20 minutes or more, and then it is quieter, more transient, and only does it after revving, while the engine returns to idle. In this case, it's so short-lived that I haven't been able to pinpoint its location with a hose stethoscope. Obviously I have not been able to use the hose stethoscope when accelerating under load.

I've already replaced the AC idler pulley, belt, AC clutch, and alternator belt. The alternator pulley is smooth and quiet, and the noise is definitely not coming from it. The hose stethoscope is how I ruled out the PSP and alternator. The AC pump was the prime suspect because the noise comes from this general area, but when the AC clutch didn't stop the noise, I really honed in on that area with the hose stethoscope. As far as I can tell, the noise seems to be coming from the engine block directly adjacent to the AC pump, but that just doesn't make sense. The oil pump could conceivably transmit noise through the block, but I haven't found any examples of anything but rattling from a bad oil pump. I'm also wondering about the main bearing, but can't figure out why this would be so intermittent. Anybody have ideas?

Can you let us hear it?

Thanks for the interest. I'll do my best, but it won't be up before Monday or Tuesday evening, after a work commute. Stay tuned.

https://youtu.be/HpHqKKarUfI

Please excuse the annoying rattling from holding the camera against the steering wheel. The car is not making this sound at all.

The video starts off with two separate clips that have the noise. Pay attention to the following play times in the video:

0:18

0:43

0:50-56

1:37

1:40

1:46

The last three events are with the car parked and the hood open. The sound is almost impossible to reproduce when the car isn't under load. I'm starting to think it could be the timing belt. This one has about 30k miles on it, and if it is, it would be the first time I've had one start to make noise.

Yeah it's hard to tell. It seems louder near the water pump or power steering pump. Maybe also exhaust leak at the manifold flange.

I can't listen to the first part. The rattle is just too nerve wrenching.

I was really looking forward to posting about solving this one with a new timing belt tensioner, but alas, after a full day of repair work, I can only confirm that neither the timing belt, timing belt tensioner, nor the water pump are the culprit either. Add that to the AC idler pulley and compressor clutch. I'm running out of rotating parts to change on the side of the engine that's making the noise.

I found this post (https://www.corolland.com/forums/index.php?/topic/23380-squealing-bad-water-pump-or-timing-belt/?hl=%2Bcrankshaft+%2Bpulley&do=findComment&comment=163749) from a few years ago while trying to figure out a better way to remove the crankshaft pulley. It doesn't really help, but I thought I'd link it for reference.

I'll try getting a better clip of the sound shortly. At this point, I'm seriously considering removing the hood and straddling the engine bay while the wife drives down the road. it seems like the only way I'm going to be able to echolocate this one. I'd consider the possibility of a transmission source, but the fact that it still does it faintly in neutral (and doesn't seem to be coming from anywhere near the transmission) leaves me doubtful.

I was really looking forward to posting about solving this one with a new timing belt tensioner, but alas, after a full day of repair work, I can only confirm that neither the timing belt, timing belt tensioner, nor the water pump are the culprit either. Add that to the AC idler pulley and compressor clutch. I'm running out of rotating parts to change on the side of the engine that's making the noise.

Late to the thread, but how did you determine that it's not the water pump? That would have been one of my early suggestons.

It was definitely not the water pump because I replaced it while I was doing the timing belt. The good news is that I do know what it was, and it's finally gone. Drum roll: Exhaust leak.

Even the mechanic I took it to, who duplicated the noise while I rode with him on a test drive, didn't believe it could be an exhaust leak, until he put it up on the lift with an assistant in the car, driving with foot on the brake (must have been fun managing the clutch) to replicate the sound. A new exhaust manifold gasket took care of it.

So with the cause definitively nailed, the chain of events leading to it seems clear. When cold, the exhaust header made a tight seal to the engine, preventing any squeal. As the engine warmed, the seal loosened, but not enough to allow acoustic effects at idle or when the engine rpm changed without load. When the transmission received torque from the engine, the movement relative to the exhaust caused the flange to open, and the exhaust leak whistled when the air velocity matched the harmonic frequency of the pipe, like an organ. The whistle also took on a secondary frequency from the engine rpm, making it sound like a squeaky bearing. Once the rpm increased past the harmonic frequency, the whistle stopped.

Thanks for posting back on what the fix was!

Wow, I'd agree with most on here - exhaust leak wasn't even close to possible suspects in my mind. Glad that you finally got it nailed down.