When the cars in motion, u hit a pot hole or the chasis flex's it squeaks and rattles! When u close the car doors, it squeaks, when u close the boot yup u guessed it squeak!
I'll give that a try, was also thinking of getting some very thin felt stuff and applying to both top and bottom parts of the spoiler. Can u tighten the allen bolts?
There should be a thin layer of sticky backed rubber between the body work & the spoiler. If it's not there trying cutting a small piece of bike innertube (or felt as you mentioned above) in the same shape & fitting that in between the body work & the spoiler.