gah!
real quick run down. in park i used to hear a noise sounded like a muffled cowbell, but i dont think its a pulley. some guy tried to run me off the road so now im paranoid about all the work i had done on steering lately (drag link,lower ball joints,damper). on the way home from work everything seemed "normal", alignment is fine.
being paranoid as i am i decided to get on all fours and crawl around the car inspecting everything. while in park and engine on, i noticed that noise similar to a bad pulley is more apparent from under the car. im assuming its a rotating part or maybe something moving along with the engine? im leaning towards a cat,driveshaft,but in my mind i wouldnt doubt it to be the transmission.
2004 ltd coupe 117k
only work i have had done is; drag link,damper,lower ball joints.
power steering pump and idler pulley x2
c(rank)ps and maf sensor

 

hey, yes sounds like if its rattling its a cat, no worries I ran my clk430 mercedes until feathers or fluff blew out the exhaust and it stopped! lol It was anoyying for a while but saved my self big bucks. Another (my recommended) option is to straight pipe it (affordable in most cases with local muffler shop, or do it right by replacing cat. Hope this helps, good luck with your xf!

 

nevermind disregard what I said, you might have some other issue but hey if it still drives and performance hasnt changed your xf might not be in that bad of a shape.