I drive a 2000 Volvo S40. I recently noticed my engine making a low rumbling sound when i reach 65 mph (thought it was just a bumpy highway at first) but when i take my foot off the gas pedal… the sound goes away.
it’s an automatic and is shifting fine.
any ideas before i take it to the shop?
This doesn’t mean the engine - necessarily. When you pull your foot from the gas the engine does change what it is doing, but this includes reduction of torque applied to the drive train. So the rumble could originate there. Axle joints are involved there as are engine & transmission mounts. If it really is only a > 65MPH thing then one would likely have to start with things affected mostly by rotational speed and connected to torque. CV joints are really what comes to mind.
Nothing else makes sense given the connection to speed. E.g. your RPMs at 65mph will be reached all the way through acceleration as you go thru each gear. If it was just engine you should hear something below 65. Though if it is from the engine my own first guess would be exhaust system related - crack/leak/break/hole in manifolds, pipes or muffler. Someone will have to drive it.