Help needed with Rattle in my floorstanding speakers.

Without knowing what speaker it is, I would suggest removing the grilles (if any) before going further. Some grille frames are steel or aluminum and may very well cause an audible rattle if not secured against the speaker or if the frame came loose at a joint.

I don't know how Simon got in there but you need to get him out.

Perhaps change your floorstanders for smaller speakers he can't get into.

I don't know how Simon got in there but you need to get him out.

Perhaps you need to change the floorstanders for something smaller he can't get into.

That particular piece enlightened me to the fact that the voice coil in my Martin Logan ESL woofer was rubbing.  I had to get a replacement from them.  It stresses parts of the system and the room so aggressively that anything prone to rattling does.  Make sure the sound is coming from the loudspeaker first, then try tightening any screws around the drivers.  I don't think you have too many options around securing things within the cabinet.  Take solace in the fact that "Fading Sun" is an anomaly amongst the tunes that we generally listen to.