Yesterday morning my Sienna 05 van was squealing at approx 70 Km/h after about 10 min of driving. What's wrong?

The disconcerting and continuous squealing would actually lessen whenever I **applied** the brake (even lightly), and would completely go silent when the vehicle turned to the right (even lightly)! This varying but all the while high-pitch sound completely stopped after the van slowed to about 10 Km/h to park, after 10 more minutes of driving. So far it did not come back to two more half-hour trips. What seemed to be the problem?