My 2 month old p400e (1k miles) has suddenly developed a rattle / vibration from somewhere behind the front passenger footwell when the engine’s running and sitting at idle revs (750rpm). It’s never done it before but has done it each time I’ve been in the car this evening. It’s quite noticeable inside the car, and when you open the passenger door it seems to be coming from just in front of the door opening. As soon as I touch the throttle and raise the revs to maybe 800rpm it vanishes and the engine’s as smooth as normal. I suspect something’s vibrating in the depths of the engine bay but goodness knows what/where. Anyone got any ideas? It’s only 2 months old so I expect I’ll need to get it checked out by the dealer under warranty but it’s a hassle I’d prefer to avoid.

mine have little rattle when the car engine is running and idel station

Anyone got any more thoughts on this? The dealer had a look last week and noticed the rear of the underneath skid plate has been damaged somehow - goodness knows how as it’s never been off-road - and thinks that it may be caused by that somehow. They wanted nearly £200 to take off the skid plate to see if that’s it, and quoted over £700 if it needs replaced, so I’ve not done anything yet as I don’t often hear it and I’m not convinced that’s the cause.

Having looked myself, there’s no sign of anything loose or rattling underneath and the noise only happens when the engine is running at tickover speed - never any other time or on any road surfaces, no matter how bumpy. When I listen under the car the noise is definitely coming from the front passenger side sill, around the jacking point.

It’s more annoying to know somethings not right, as it’s inaudible >95% of the time, so I may just try to live with it on the odd time it happens, but any ideas of causes are welcome!

If the dealer is claiming that there's damage from off-roading and you know it's never been off road, ask them to show you on the car exactly where the damage is. Sounds like the usual main dealer fob-off. They'll charge you to "investigate" it, do nothing and leave you with the rattle and a hole in your wallet.

Likelihood is that a bolt is loose and vibrating at idle. I bet if you jacked it up (trolley jack and then axle stands) and had a look yourself, you'd find said loose bolt. Alternatively, a stone has ended up trapped somewhere. 2012 SDV6 - it's missing a couple of cylinders
2008 TDV8 - it was a labour of love and is much missed

I decided to call out LR Assistance to take a look in case there was anything serious. Within about 10mins the guy found two plastic pipes/tubes which he thought were likely something to do with air con which were vibrating and touching together behind the front footwell when the engine was at idle. One cable tie later and the problem is solved. Brilliant job from LR Assistance!