Gear Rattle / Chatter Sound When Car Is Idle, in Neutral, and the Clutch is Not Pressed Down (Potentially Air-Con Related)

I am experiencing what I can only describe as a rattling/vibrating noise from what sounds like the gearbox of my 2007 Ford S-Max (1.8l TDCi), which has done 87,000 miles. It's a manual transmission.

I've owned the car for two years now, having originally bought it with 67k miles on the clock.

The noise is only present when the car is BOTH idle and in neutral. It remains present until I press the clutch down and move from neutral into ANY gear.

As soon as I do the above, the noise disappears. It then resurfaces when shifting back into neutral and taking my foot off the clutch.

The noise DOES NOT disappear when pushing the clutch down. It's only when then moving it into gear that the noise goes.

Equally, just a gentle touch on the accelerator pedal seems to stop the noise - even while the car is in neutral and without the clutch being pushed down. When the accelerator pedal is released, the noise resurfaces.

The clutch seems fine to me. I don't struggle to get the car in gear, there's no slippage, and I haven't picked up on any of the other telling signs to suggest my clutch is on its way out.

The problem described happens around 80%-85% of the time. There has been the odd occasion where the engine is idle and the car in neutral, and the noise isn't present. When that's been the case, there has been nothing different of note to help me troubleshoot why it doesn't happen 100% of the time.

Interestingly, the problem has only surfaced this past week. More specifically, I've just had a new passenger-side windscreen motor and indicator stalk fitted. The Autoelectrician had to do some "reprogramming" to get the new windscreen motor to work, which mysteriously caused my Air Conditioning to work, which had never worked before.

Now, I've seen a few threads on other car forums - Mazda, Toyota, and Mini, especially - about the possible link between the issue I've described and the A/C compressor, but nothing concrete to suggest there's a link between the two. More the fact that the extra load on the engine caused by the A/C could be making the noise more prominent.

I've experimented with/without the A/C on, but the noise almost always seems to be present, regardless.

Even with the factory-fitted Sony radio on a level as low as volume 7 or 8, you can barely hear the noise in question. When the A/C is on, too, it's impossible to hear. It's only when you have both switched off and all the windows in the car done up that it's just about audible.

The noise is, however, concerning (and annoying) enough to warrant seeking advice from anyone else who has experienced this before.

Having just forked out £1k on genuine Ford parts (£550 alone for the bloomin' windscreen motor due to being unable to source a working, used equivalent!) and labour at my local garage for the other fixes to the car, I can't afford to spend any more on it right now, if it is something that I am safe to live with for the time being. Unfortunately, buying a new, used car isn't an option with three young kids to care for.

Any help or advice would be greatly appreciated. Thank you.

Hi there , I have a similar issue to you , which I believe to be worn gearbox input shaft bearing , more pronounce when ac is turned on , just wondering how you went with this ?  

Apologies for the late response. I ended up having to replace the Dual Mass Flywheel. It fixed the issue, and I've had no further problems since over a year later.

All good I’ve just seen your reply , we all live busy lives