At about 6,000 miles on my 2013 Tacoma 4X4 I started hearing a growling noise. I brought my truck into Desert Toyota here in Tucson and the service manager said it was the tires making the noise, which it seemed like it could be. When I reminded her they only had 6,000 miles on them she said, " you are not the first person to complain about the noise". So I went down to Discount Tire, they checked the depth of the tread and told me the tires were worn half way down, I explained, they were new tires and was told Toyota puts a cheep tire on their trucks and that the growling noise was tipical of BFG tires when they are worn down. Ok, so I put a set of Michelin LTX tires on the truck, when I drove away, I was PO'D, the growling was still there along with the vibration. Let me explain, some times there is no growling or vibration and I love driving the truck. The following day I brought the truck back into DT. Their machanics could not find a problem. A week later, I brought it back again, and the first service manager went for a ride and said she could hear and feel the problem. I Gave them my truck for a full day and again they could not find a problem. Again, I brought the truck back, and the second SM went for a ride and said he felt and heard the problem, but because it was intermittent, I would have to wait until it got so bad they could figure it out. Well, I'm still driving it and now it has become mostly a vibration in the steering wheel, that is very irritating. it has become more intermittent and is driving me crazy? There is 8,500 miles on the truck and DT is assuring me that it will be covered under the 100,000 warrenty, I can only hope this problem will become obvious before the warrenty expires. Anyone out there have an idea what it could be?

Thank You