Identifying a Ringing / Singing Noise when the car is travelling at 30mph+

[Bourne]

I’d appreciate a second option from this forum on diagnosing a noise I’m hearing in my MGB.

When I have been driving for some time, I often begin to hear a faint ringing noise within the car. It gets more noticeable above 30mph and seems to be appearing when I am using the accelerator pedal.

Running the symptoms through an AI tool (not that I trust AI’s accuracy, but it is helpful getting a handle on novel symptoms) it suggests the issue is the u-joints on the prop shaft and that the ringing (or singing) noise is resonance caused by early wear in the joint. This would seem to make sense. I have the dreaded occasional clonk in my diff which I have learned to live with. That might have caused the u-joints on the prop shaft to begin degrading. I also noticed when I ran my cloth gloved fingers along the prop shaft that the noise made is very close to the ringing / singing I can hear. I haven’t been able to replicate that sound on the front or rear axles.

Are there any alternative causes of such a ringing / singing sounds I should be looking into though? Before I was put onto the path of looking at the u-joints, I was hunting for a rotating metal part brushing against something. Could it be vibration created elsewhere travelling along the prop shaft?

If it is the prop shaft u-joints, how much of a problem is that? This old forum thread suggests that can be lived with for years (assuming its the same issue), whilst other parts of the internet are more alarmist (“Stop driving the car immediately”). I have been noticing the noise for over a year now, and I don’t think its getting significantly worse

Thanks

DB

[Ian F]

David, I would normally associate drive line wear with rumbling noises or a rythmic thrumming - quite a low sound rather than ringing.
You could take off the battery cover and take the car out. That should help identify transmission noises.

Are you sure it's not from the front of the engine? That kind of sound I usually think of timing chain, dynamo, alternator, water pump etc.

Of course it could just be a loose bit of metal somewhere just rattling/vibrating!

Ian F

[Bumpa]

Another thought is, could it be a disc brake pad just kissing the disc as the wheel rotates. The clearance between pad and disc is tiny at the best of times. The disc could be made to "ring" like a wet finger on a wine glass.

[Ian F]

Thanks Mike. That should be easy to investigate by lightly applying the brakes whilst listening to the ringing noise.

Ian F

[Bourne]

Ian, Mike, thanks for the thoughts on this. I took the car on a 25 mile drive this evening listening to the noises it makes. Turns out there are two noises.

The is a high pitch ringing / singing sound I’m inclined to agree with Ian is a lost fastener in a boxed off space. I know of at least one nut in the box space under the seats and floor. There must be more! I’ve had such “Foreign Object” noises since I bought the car and whilst they are annoying, they obviously aren’t an indicator of a problem.

The second noise however is a lower tone Something akin to a scraping noise. The noise is also intermittent and inevitably doesn’t appear when I want it to. I put the car into neutral but that didn’t change the noise (rules out the gearbox). Breaking also didn’t seem to affect the pitch or tone which suggests it isn’t the disk brake pad (I’m still going to check out further Mike’s idea though - my brake discs and pads are safe but nearing end of life and it’s plausible this is a symptom). The sound appears speed affected, but tapping the accelerator pedal doesn’t in itself make the noise appear or disappear. That suggests the problem isn’t in the Diff.

I wonder if it could be early wear in the drivers side wheel bearings? The noise seems to come from the right direction from where I’m sitting.

[Paul Scott]

Mine had a sound like a bird twittering once.

I adjusted the bonnet spring, noise went away and has not reurned.

Paul