Sound coming from the exhaust of my1997 NISSAN ALTIMA?

I had taken the car to monroe muffler and they said it's because of the exhaust.''The parts from the cat down is rusted and has to be replaced ,costing about 500$''.Now I had a friend take a look and he clamped a pipe in between the muffler and something ,and the sound has decreased a lot.So what according to you is the parts that need replaced.I am planning to buy them cheap somewhere and ask that friend to replace it.





Please advice!Thanks|||It could just be that you need to replace one of the hangars, that's only about $10.





That's honestly a little bit of wishful thinking though. Odds are that you need a new catalytic converter, aka, cat. The purpose of the cat is to restrict airflow and increase the temperature of the exhaust gases. Increasing the temperature burns off more of the toxic fumes and makes car emissions more eco friendly. The cat restricts airflow by using a ceramic honeycomb that's inside of a box in the exhaust pipe. After several years of use (or sometimes much earlier if there's a problem with how the engine is burning fuel) the honeycomb will get clogged, when it gets clogged it breaks apart and rattles. That's probably the sound you're hearing. Eventually the cat will get clogged up more seriously and that will cause problems with idling rough and stalling.





To help you be sure that's the problem I'll give just a little more info. The best way to find out is just to listen where the rattling is from. If it happens at idle, just put the car in park and walk around and listen. If it happens more at a certain RPM get a friend help you by holding the accelerator at that RPM while it's in park, now walk around the car and look for the rattle. The cat is usually somewhere under the front seats, generally under the passenger side front seat. If your search leads you here, that's probably it. Turn it off and wait for the car to cool thoroughly, remember the cat gets very hot. Now to be absolutely positive, bang on the cat once or twice with your fist with the car cooled down. If it rattles, that's it.





Cat's range from about $250 - $1,100 installed depending on what kind your car needs. Some Fords, like Mustangs, have an "x" cross pipe have two cats and two resonators that all have to be replaced at once if any one part goes bad, very expensive and stupid design.





The sound you have absolutely isn't because you need a new catalytic converter and a new muffler, that's what "from the cat down" would usually mean. Take it to another shop after you've done the checks I talked about.





One last thing, if it is the cat, cars in america have to have an 8 year 80,000 mile emissions system warranty that will cover it.|||First things first. Usually, it is a poorly tuned engine that causes the exhaust system to begin failing. If the fuel mixture does not burn clean enough, the excess will eat holes through exp[ensive exhaust components. secondly, NEVER waste your money on aftermarket junk bought grom muffler shops. It is not designed for YOUR car, you just waste more gas and lose MPG's. Keep your engine tuned properly, and keep your idle air control valve and throttle plate clean, This will optimized fuel mixture and extend exhaust system life. You should also be using Platinum or Iridium/titanium plugs in this thing. Try to have your system patched if you cannot afford the genuine Nissan factory replacement parts. Genuine parts are the only way to do this thing right, believe me!!!!|||If the sound is a low down rumble then it is merely a hole in the exhaust due, probably, to rust. The cat is palladium and is pretty well bullet proof so all you need is a replacement rear end for the exhaust or a home sealing kit if you're competent enough to do it yourself..|||Really, how could anyone out here know without looking at it? Take it to another shop, tell 'em you're broke and need it fixed cheap. Most places will patch it up if that's the opportunity they have.