Car shakes only at 55mph

My 96 Camry (100,000 miles) is shaking when I hit 55mph. I took it to a mechanic who said it was the tires. I took it to a tire place and he said the tires were worn, but not causing the shaking and it needed a mechanic. Took it back to another mechanic, he replaced the engine mounts. Still shakes. Replaced the tires (cause I needed new ones) got it aligned. Still shakes. Took to a third mechanic who checked some things but couldn’t determine why it shook.

Could this be a 55mph resonance frequency? At a certain speed the car shakes because the belts moving and such oscillate the car. It’s been doing this for the past 40,000 miles. I’ve just been avoiding this particular speed.