Running without wastegate muffler

Hi, as you probably know by now I have a '86 911 turbo, I've had a annoying rattle comming from the back of the car, it sounds to me like exhaust / muffler rattle, it ushally happens on tickover, waiting at the "takes forever to change" N.C. traffic lights. We thought it may have been inside the wastegate muffler, so we removed it, and I am now running the car without w/g muffler !
Q1/ What exactly does the wastegate do ?
Q2/ Does it have a cat in it ?
Q3/ How will this affect the running, ie Can it do harm to the car or will it increase/decrease the HP ? - the turbo seems to realy kick now !!
Q4/ I have heard that some people put just a pipe on instead of the muffler, is this a good idea ? I think I can get this "pipe"
from Powerhaus for about $100...
Good Idea Y/N,
Oh and last but not least, I still have the damn rattle, any ideas...
/Paul

Here's some info. 1- The waste gate controls the boost pressure, i.e. it opens at .8 bar on stock systems or you can install an electronic valve controller such as HKS to allow boost to be adjusted. 2- Yes the little muffler looking thing is actually a cat and is required for smog purposes. 3-Running with the pipe off will just allow the gases to blow onto the underside of the left rear fender, engine, etc and make the car not smog legal. 4-As for the rattle, check the mounting bracket from the stosk system to the engine or remove the stock muffler/cat and shake it as a baffle could have broken loose inside. Try listening to the system with a stethescope or long screw driver to see where the noise is.

I Have replaced the stock muffler with a stainless sports exhaust / muffler without a cat, Thats why I thought it was the ceramic breaking down in the cat on the wastegate as Its the only cat on the vehicle (not any more) as I had a simmilar rattle I got when my Jeep cat was shot !!