Nissan Quest - tire problems?

I have a 2000 Nissan Quest SE. 1 month ago took van in for tire rotation. Shop said inside of rear tires were grooved with a circle cut. Shop adviced to replace rear tires and have them aligned. Rear tires were replaced and aligned. Problem continues - when driving at speeds over 40mph the inside of the van has a humming or wa wa wa wa sound. The steering vibrates slightly. Just got new tires and had the alignment done.

Any idea what is causing the humming or wa wa wa wa sound?

Derekvrichmond
June 2004