2019 outback base noise @ 35-40mpg

[oldolr]

At around 20 to 30 to 40 mph I hear and feel, base type sound similar to what a pre-amp or a kicker box might put out in car stereo. If you accelerate slowly this sound is very noticeable, you accelerate faster, not so much. Iv'e taken it to Subaru Ft worth and they are clueless. Anyone own one of these and have you experienced this annoying sound or anything similar.