Loud squeak behind instrument cluster

Weather around here finally relented and I was able to get the XJ-S out for a drive. I was immediately reminded of a project I need to get done. There is a horrible squeaky noise coming from behind the instrument panel when the car is moving. It seems worse at low speeds.

Last fall I had thought it was the bonnet but I tightened that up and the squeak remains.

What the heck is behind the instrument panel that would chatter so badly?

Thanks,
Matt