2004 Acura MDX Shaky Steering and Interior Lights dim every

I just bought an Acura and drove it on the highway and noticed that once I go over 70, the steering wheel viberates and my interior lights dim for a few seconds then come back on.

I was told that a tie rod needed to be replaced as well as my battery. But the dealership had his mechanics look at it and he said that there was nothing wrong with the tie rod or battery and that battery was under a year old anyway.

I'm getting a third opinion.