If you are not under warranty, I think the VW cats run around $800 for the part alone. As for it being a mandatory repair??? Well, it's your car and you can do whatever you want with it. Depending on what state you live in, most likely, keeping it this way will cause it to fail the smog test.
Basically, if your cat is inefficient, you are driving a car that is more polluting that it should be. (Think of global warming!) That noise you are hearing is the inside of the cat breaking up. Worse case scenario is that it breaks up to a point where it gets clogged on the inside and can create a whole bunch of other problems. e.g. missfires
If you take it back to the dealership, make sure they do the software update for "the other" cat problem as well. It basically makes the check engine light less sensitive to throw an inefficient cat code when the cats are okay. (In your case, the noise you are hearing is a confirmation that the cat is bad.)
Good luck.|||You have to have a Catalytic Converter unless it is under 1984. Thats when it became mandatory.
|||Well, it all depends on your state. Some states don't have any kind of emision testing. ie Mississippi
As far as having to replace it is really up to you. A messed up exhuast system can affect your gas milege as well.
Common in those cars? I work for a VW dealer and I havn't seen "alot" of beetles with bad cats. Doesn't mean there isn't any out there, but... Have it checked, you can go to a part store like Autozone and they can do a diagnostic on it and tell you exactly what code your car is throwing you. From there decide what action you want to take after you find out a little better what it can be.|||a rattling noise? the "cat" is worn out and needs to be replaced.|||you can get the code read at the dealership. it will cost a few hundred dollars to replace if it is the cat. you need the cat so you can pass emissions tests (and not harm the environment). you can also go to autozone and get the code read. write down the code and type it in to google like "vw code (whatever the code is)" it will come up with results for forums and things like that where people have had he same problem then you can know what you are dealing with.|||You would be totally lucky if you live in California and your car is less than 8 years old and has less than 80 k on it,cause then it would be emmissions warranty. Other wise it would be a good idea to replace cat if it is rattle,as it fails pieces of it could plug muffler.