After my 2005 MCS got rear-ended, the body shop replaced certain parts of the exhaust after I complained of it rattling at idle. Now that some of the exhaust parts were replaced, the rattling is gone, but the sound of the exhaust is waay different than before. It's more of a deep bellowing when the engine is revved now and it's so loud and deep that it rattles interior parts a bit. The replaced stock exhaust just sounds out of tune and louder than when the old stock was on. I know it's not right, but I could not find anything visually wrong with thier replacement.

However, the body shop told me that they replaced everything from the catalytic converter (excluding the cat) backwards. What I saw when I looked under there was that they replaced everything from that 'can' looking thing (resonator maybe or it could be the cat) to the first muffler. They did not replace the second muffler that feeds off the first muffler and the dual tips are connected to.

Could this be where the problem lies? I would think that with an old broken-in muffler coupled with a brand new one would not be tuned correctly. Do mufflers have to be replaced as a set for the exhaust to keep its stock quiet tone? If so I'm guessing I am within my rights to make them do the job right and replace that other muffler.

Thanks!

 

That "first muffler" is just a resonator. It has a different internal construction from the other one.

I'm not sure if an old muffler and a new resonator would make it louder. How bad was this accident? Maybe there is no more sound insulation due to the new parts.

 

Thanks for the quick reply. I just got the car back today and I'm anxious to either get them to finish the job right or just deal with it if something has to break-in.

Regarding the sound insulation, all I saw when looking under the car was heat shielding. I didn't see any insulating material. Should there be and if so where would it be located?

The accident itself was not bad. Just a new hatch and repainted quarter panels. The exahaust sounded fine even after the accident. It was their decision to replace exhaust parts when I complained of rattling after the accident repairs. I personally think just a heat shield peice was bent but what's done is done. I'm pretty sure this new badly sounding exahaust has something to do with the fact that they replaced one muffler/resonator and not the other. Or maybe what they replaced has to 'break-in' to sound better. That's what I'm trying to figure out.

 

Seems unusual that they would change just one rear muffler. Does the new rear muffler looks just like the old rear muffler? Is the new rear muffler a original equipment replacement muffler, for example can you see a Mini or BMW stamp on the muffler?

The resonator in the muffler in the middle of the car. It is not uncommon for the resonators to develop a rattle.

Maybe the repair shop had the muffler and resonator replaced at a muffler shop with a non-Mini parts. That could make a sound difference.

 

There is no sound insulation under the heat shield. I didn't know if you had any on your hatch or inside the quarter panels that is now gone. But since it was fine after the initial repairs, this is not the case.

 

Yes that 'can' muffler in the middle of the car which is the resonator they did not replace. They replaced piping from that on backwards to that first muffler in the rear. When I had a look underneath, nothing seemed visually wrong and the muffler they replaced I'm pretty sure had BMW p/n on it. But I could definitely tell they didn't replace the other muffler because the piping is all rusted and muff is worn like it has 53K on it still.

So since they didn't replace the resonator and the exhaust sounded fine before they replaced what they did, I think the res can be ruled out.

I know the adjuster will think I'm an sob for asking (will make the 3rd time I asked the car be returned to the body shop) that the other muffler be replaced, but will most likely do it if I can convince that this new muffler is conflicting with the old. I could care less anyway if people think I'm an sob when it comes to my Mini being fixed the way it should. However, I need to be sure this is what's going on.

 

If it sounds different than before the accident, you have the right to have them make it right.

 

Did the body shop use OEM parts?

 

Yes they used OEM Mini parts, just replaced one muff and not the other. Still debating wheather or not to call up the adjuster again to get them to replace the other muff.

Can any muffler experts on here that can tell me if you replace one muff and leave the other with 53k miles on it, could it throw the tuning all out of whack? That would be my argument.

 

No way to alter the tune of the car with an exhaust repair.

All they did was replace some tubing and the resonator (passenger side). If the sound changed that drastically they must have done something more.

 

I get the same sound from my exhaust when an intercooler coupler is leaking, or when I remove the plug at the back of my DFIC intercooler........my exhaust sounds like a Sherman Tank when that happens.

Check for vac leaks.