I've done a bit of searching here about this and couldn't come up with anything definitive so thought I'd pose the question - apologies if I've missed a previous answer.

I've noticed in the last few weeks that when I pull away in first, I'm getting a sound almost like the gear is straight cut - it's a low whine that increases in pitch as the car speeds up. It's slightly present in second too, but to a far lower degree. Outside of that I haven't noticed it, and there seem to be no other ill effects.

I've been told that this suggests a diff bearing problem, and that even though it's common it can still be pricey to fix. Anyone got any thoughts or experience concerning the symptoms and the price of putting it right?

Diff bearing would whine in all gears, as would an input shaft bearing. That leaves the output shaft that 1st and 2nd are on, along with 3rd and 4th.

So it is more likely to be actual gear bearing, or selector fork running in syncro sleeve. If high mileage a gearbox oil change should help. Also selector cables may need slight adjustment.

That's an interesting thought - there does seem to be a bit of judder when you touch the gear lever to change up from first. The car has only done just under 80k, not sure if that's considered high for the gearbox oil. I'll have to take it out later and wind it up through third, see if the whine actually is there but is masked partly by the engine.

Cheers for the feedback, much appreciated. Do you know what sort of work (and cost) is involved in nailing the sort of issues you've suggested?

Gearbox specialist charge about £350 to recon a gearbox, but that price does not include removal and refitting. Although Skoda say box is oil filled for life, even Hypoid oils break down over time, so an oil change may well cure it. You could also add some Forte diff treatment with the oil change. Brilliant stuff, and you may well end up fixing it for £20 all in.

I've never had much success rebuilding boxes (Morris 1000 A Series ones), always find they just make a different noise

Although a noise can be annoying, the box could well do another 100K no problem.

If you do have the box rebuilt, ask to have the crown wheel rivets removed, and stainless nuts and bolt kit fitted. At high mileages, it is not unknown for the rivets to shear, and the crown wheel chews a rather big hole in the gearbox casing.

That's worth knowing, thanks - I'm having a few bits and pieces done soon, so I'll run that past them. I went out today on the backroads, and inbetween loose 'repaired' surfaces and 38mph Corollas managed to wind it up a bit. It's impossible to hear if the whine carries over to third because of the increase road noise - it's not dramatic enough to cut through - but it's definitely there in first and second.

Would it narrow it down to the diff or gearbox if I was to spin it up through first, then cut the throttle and step on the clutch at the same time? If the noise falls slowly with the road speed would that point to the diff, rather than the faster decrease in volume I'd expect from a gear bearing? Or would the difference between the two not be that noticeable?

Generally speaking a diff bearing will whine in all gears, sometimes under load, most often at light load cruise speed, and change whine note on the over-run. A really shot diff bearing or out of mesh crown wheel and pinion, will even whine while coasting in neutral.

It can be tricky narrowing a whine down, as when you dip the clutch, the torque changes direction, as the road wheels drive the gearbox, rather than the other way round.

An output shaft main bearing will tend to whine under load but be quieter on over-run. A whining gear bearing will go quiet when you select the gear that has the faulty bearing. This sounds strange, but the gears are all in constant mesh (except reverse.) When you select a gear, the syncro hub which is a splined fit on the output shaft, locks the gear to the shaft, so it's free running bearing no longer gets rotated. Non selected gears run on needle roller bearings, so in effect they are free to rotate independent of the output shaft.

It's little wonder that the humble gearbox will confuse even a seasoned mechanic

BTW, if road noise is drowning out the whine, I wouldn't worry about it. My Moggy has rather loud diff whine at 50MPH+ and even the stereo wont kill the noise. If I could find my box of shims for the pinion, and engineers blue to check the mesh is correct, then find my load gauge to check the pre-load, I would probably fix it, again. Being 1969 technology, it would simply go out of whack again in 12,000 miles

Been trying to work out which of the suggestions is the most likely over the last few days, and not getting very far. I'm now pretty certain it's only noticeable in first and very slightly in second. When you take your foot off the throttle in first the noise continues exactly as before but just decreases in pitch as the speed falls.. just like with reverse There's no noise whatsoever in neutral, which is something at least.

There doesn't seem to be any ill effect apart from that - the gears select cleanly, although there is a slight graunch when you first take up drive and the engine comes under load - this disappears after a couple of hundred revs, although it can happen in any gear if the revs fall low enough.

It's all very odd, and mildly irritating

When you take your foot off the throttle in first the noise continues exactly as before but just decreases in pitch as the speed falls.. just like with reverse There's no noise whatsoever in neutral, which is something at least.

When you say no noise in neutral is that at a standstill or if you're rolling with the noise present and move from 1st to neutral and coast?

Both - it idles perfectly, the moment you dip the clutch the sound falls off, and remains so throughout neutral. Putting these three together and noting that it doesn't only vanish in one gear makes me wonder if the earlier suggestion was right and it's a shaft bearing. If so, would the noise would be loudest when a gear was engaged closest to that bearing?. If I'm reading it correctly the symptoms would suggest it wasn't the diff. I was interested by the suggestion that it might be a selector fork, especially as it only seems to happen in first and second, but I'm not sure how that would create this particular sound.

Would that brief grumble when taking up the load at low revs commonly be found with one of the aforementioned faults?

Been trying to string out the time before getting this sorted due to cash, but now the plot thickens..

I noticed a couple of days ago that the transmission seemed to be a bit more rumbly than usual, and the graunch from low revs a bit louder. If I accelerate in first gear and then back off on the throttle whilst touching the gear lever I can feel a lot of knocking coming back through it - this doesn't seem to happen in any other gear, although it could just be the higher revs it reaches in everyday driving.

To add to that, I was on a dual carriageway today in 5th and moved to overtake a rather erratic people carrier when I noticed that under power it felt as if a wheel had gone out of balance with a shake coming back through the steering wheel. Backing off on the power slightly instantly made it disappear.

Does this sound horribly diff-like? If so, how much is it likely to hurt my wallet, and is there any real benefit in fitting as LSD on an otherwise unmodded car?

Ive been noticing a whine when i back off the revs or slow down for a roundabout or up a hill to a junction. Hope its not anything serious! Doens't seem to make any noise when driving, or none that i've noticed above the road noise. At first i put it down to the rubbish tyres i have on the front and increased noise from them, but a bit more concerned after reading this,