humming at motorway speed and vibration

[Charlie Chaplin]

Hi guys,

When i am driving my RX 400h, at motorway speed, there is humming and vibration.  It starts after 50 mph. That noise and vibration go when i decrease my speed to 40 mph and it won't come back even if i accelerate. next journeys it happened again. It started with just a tiny humming and now the humming noise increased and the vibration is added. when i brake, there is no pullover or any other problem. i am suspicious about my front tires because they are cheap :)) does tyers do that or does anybody have any idea about the problem, please?

[Spock66]

Wheel balancing would be the first thing to check.