2006 S40 VERY Loud Engine Noise Off and on While on Highway

[mjabramson]

I have a 2006 Volvo S40 with 140,000 miles. For the past month or so, when driving on the highway, the engine seems to get very loud off and on. Nothing consistent with accelerating, slowing down, etc. It is so loud I feel the vibration and the panel where the radio, heat etc. are seems to even vibrate a bit. I say the engine because that seems to be where the noise is coming from, but it could be the exhaust. Again... I don't think it's the muffler because it comes and goes. And doesn't seem to happen while driving slowly. When I park the car, idle, gun the engine etc. with the hood up it doesn't happen. Any guesses? The only thing that changed just before this started to happen was that I switched to a synthetic oil blend during an oil change at the recommendation of a quick lube place. Also... while idling in park the engine does have a light rattle to it.

[mf70]

Perhaps you can record it while underway, or run the car while on a lift & explore with a stethoscope...