Plastic sliding noise under seat

[djwoody]

I have a noise under my drivers seat that is driving me insane.
Every time I put my put down or brake, go round a corner there is this plastic sliding sound.
I've checked everywhere, even had the air duct under the seat out just to make sure nothing was caught in there.
If there was something sliding round the undertray would you hear it in the cabin?
any ideas people?

Thanks
Chris