My bike has started intermittently making a strange sound somewhere around 7k.

It is kind of a hollow higher pitched metallic vibrating sound. sounds like the normal engine rev only higher, louder and kind of tinny.

From where I sit it seems to be coming from the engine under the tank somewhere.

I have not been able to reproduce it while sitting in the garage but it can happen while riding in any gear or with the clutch pulled in.

The bike starts, idles, runs, accelerates perfectly. Oil is full and changed about 1000 miles ago.

There have been no changes other than the noise, but it is pretty loud and I am scared something is about to break.

I realize that from my description it is probably hard to tell what is wrong. I am hoping this happened to someone else and they will know exactly what I am talking about.

do you notice it more or less with a full tank of gas?  you may have lost a rubber from under the tank.

Is your gas tank cushion on the frame there and installed correctly?

-Jessie