A few years late to the conversation, but i figure it may help someone later on. My 2015 Volvo V60 experience the same rattling during acceleration and it turned out to be a small crack in the exhaust manifold. Replacing the manifold in extensive job due to the location and surrounding components. To add insult to injury the exhaust manifold is sold as one unit along with the turbo component. So you will pay anywhere from $1800.00 to $2500.00 USD for the replacement part. Hope this helps. Good luck to you.