It's normally when I am on the break and I turn the steering wheel to the left. Less often to the right. I hear this knocking noise that has me thinking something is loose. I also hear something rattling in the rear when I hit a bump (NYC driver, can't help it). I just got my boy in April and he has been great. But I'm starting to think that the City driving is taking a toll on him. Former owner was a suburbanite. Is anyone having the same issue.

 

Its a common issue for the ES. Theres a TSB on this issue from Lexus.
The steering intermediate shaft needs to be removed and lubricated. Take it to your Lexus dealer and they can easily fix the issue for you.
Mine did the same thing, and i simply removed and lubricated the steering shaft and its been perfect since.