Well, you can do 157 in 6th....so..... I couldn't really tell you what gears and what speeds, I just listen to the bike, and when I do glance down, it is just to check my speed, or to look at the tach. I'm going on a ride tomorrow, so I'll try to pay attention to what speeds I shift.
Think of this though: If you put your bike in 6th at 35....that means you could ride it all the way out to 157, let's say 160. That means you are using 125mph worth of gear! What are all the other gears for?
I'm not trying to tell you how to ride your bike, I'm jsut trying to tell you that 6th gear at 35, or at any in-town speeds is a little....different.
Is the sound coming from under the gas tank, or from the rear of the bike? Is it a tick, tap, knock? Does it do it when you are stopped, or only when you are riding?
Have you checked the chain tension? It's in the manual.
How many miles are on your bike?