About 5 days ago I noticed a vibration under light acceleration in my Titan kingcab. It begins around 10mph to about 15mph then goes away but comes back again from about 30-35mph then goes away again over 40mph. I thought maybe I had irregular wear on my front tires so I wasn't worried about it because two days earlier I had ordered another pair of Wrangler SRAs for the rear and was going to move the one year old rears to the front. However when replacing them on Saturday it didn't change anything. I bought the truck 3.5 years ago with 76k miles and immediately changed the diff fluid and paid a Nissan dealer to flush the tranny. Both should still be good for at least another 25-30k miles. I can't quite tell if it's coming from the rear or the front. Last week I thought it was the front but now I'm not sure after the new tires. Any thoughts out there?