Deep/lowbass engine sound when idle or accelerating
 

Hello. I've got a 2015 honda civic with 42,000 miles. Bought the car last year and it's been great. About a week ago I noticed a change in engine sound when on idle or accelerating above 50mph. When the cars on idle it sounds like a deep low bass sound,like there's an issue with the exhaust or a leak. When on the highway the sound gets louder as the car speeds up. It's a cvt transmission. The car drives excellent. I feel no issues with the transmission and the engine is really smooth. I took it to a muffler shop to check the exhaust and everything was good. No leaks or any damage. I also feel a little bit of vibration when sitting on the car but maybe that's just me. It's a 10 year old car but it was maintained in excellent shape. I got the car with 36,000 miles and it's been seven months with no issues until this sound now. Any similar situations? Thanks