not sure if its the same noise mate but i had noises along the same lines on both my previous rs after fitting mongoose system the first one turned out to be the support bracket just gently tapping the the sill behind the drivers seat on tickover the second seem to come more from the front of the car and only happened when cold and ticking over , then one day i took the system off while waxoiling the car when i refitted it it was no longer there the only thing i could put it down to was the heatshield under the car catchin , but cant be certain