When our XC90 is at idle sounds like a diesel with check engine light on.

The check engine light needs to be scanned to find that fault, the noise needs to be looked at by someone who can find the issue. Then post that we can help at that point.

I've been reading up on timing chain problems and signs of them. The XC90 3.2 has a timing chain. Typically when a chain is going bad it becomes somewhat loose due to tensioner problems and it can sound very loud, like a clattering. This obviously could be the problem. Advice on blogs is to not drive the car as chain failure can destroy the valves. Typically this could be a $1200-$1500. fix. The odd thing is that timing chains in the past were only required to run one cam and could easily last the life of the vehicle with no issues. Today many engines have as many as four cams. Cadillac SRX V6 for example, which has had a history of chain problems has four.