I get the steering wheel shimmy/nibble on my truck. However, it doesn't happen all the time, and when it does it goes away after about 5 minutes of driving. Pro'lly flat spots on the tires from sitting parked. OEM General 17 inch tires.

 

I would give it back if the problem can't be fixed. I have the bed cha cha too rattles tail gate but not not a cause to take back. I have the stock 18's on a flare and smooth ride at any speed.