Hi All - I have a 2006 S40 T5 with 120,000 miles on it. Lovely car, but always throwing a new mystery at me. I've noticed within the last few weeks that on a cold start-up (in a New England winter), it will often start making a very rapid ticking or rattling noise. It seems like it's coming from behind the center console. I hear it quite clearly in the cabin, but have a hard time making it out when standing outside by the engine. It will keep ticking for a few minutes until the engine is warmed up. Oddly, even if I turn off the car, it keeps on ticking for a minute or so. It started off only happening occasionally, now it happens on most cold starts (the weather has also gotten more consistently cold). Any ideas what this could be?

 

Given you say it ticks after the engine turns off suggests to me its probably one of the heat shields (like that shiny plate that sits between the firewall and the turbo/downpipe) ticking as it expands or contracts with warming/cooling. They are also located under the floor around the cat and exhaust (cat's get quite hot ~500F to operate ).

 

Thanks for the reply! I will look into that idea.