F31 320d noisy idle - any ideas?

[Martin996]

I’m hoping someone out there may have had the same thing. My 2014 320d has developed a notably noisier idle. It sounds like the normal diesel idling sound just is much louder in the cabin. It’s barely perceptible from the outside. The noise goes away above 1000rpm.

My initial research suggested saggy engine mounts that were no longer isolating the engine and its vibrations, so I replaced those and it made no difference. I then replaced the crankshaft pulley as that has a damper in it, but that also made no difference.

I’ve had a good look but I can’t find anything that’s loose and vibrating, but that’s exactly what it sounds like. The timing chain is quiet, with no rattles, swooshing, etc. The idle is smooth and there is no misfiring.

Has anyone had a problem like this and solved it? Does anyone have any suggestions to help diagnose it?

[_Hoppers]

A complete guess here - Do you have high back pressure at the DPF?

[AlexGSi2000]

My f11 530d does this - its quite annoying.

Its more prominent on colder mornings. During the summertime or above 21c outside temperature its barely noticeable.

I have replaced a lot of the rubber fixings on the engine covers.etc but it still remains - next I was going to try the engine mounts.

Have you tried the transmission mounts?

For me, it sounds like the noise is originating behind the dash - to be fair I really need to spend the time going over it, it really does sound like a plastic panel resonating somewhere.