carterleeds

hi guys just got my mtm exhaust back boxes fitted and they sound great however i have a slight problem...

when i drive it on the motorway and stay at a certain speed and RPM, i have this nasty drone/humming/bellowy noise in the car which is caused by the exhaust. only thing changed was the back boxes everything else was left stock.

so my question's are... 1. what can be done to resolve this noise issue apart from removing the back boxes (if needed will be done though). 2. why am i getting this bellowing noise in cabin?

thanks in advance

ltooz_a6_a8_q7

Why did you put this "Black Box" into the car? What was it that you wanted to improve or destroy?

The logic is this, if it works before - noted everything connected - modified something - outcome changed - removed what was changed - test again - if it works - throw the changed part away or accept the modification outcome.

Cheers,

Louis

snapdragon

I suppose the new ones must have a resonant frequency that clashes with the frequency generated by the engine at certain RPM and causes a harmonic that would be 'engineered out' by factory engineers during R & D.

carterleeds

3 points!!!!!!!!!

firstly you obviously haven't read the question properly or else you would know what im talking about and replied with a suitable solution or just replied within context like snapdragon.

secondly if you dont know what im talking about why have you wade in for?

and thirdly i would appreciate it if you first read the post and then kept your unhelpful and useless comments to your self.

cheers,

carter

carterleeds

yeh i thought it may have something to do with the pressure. i may just unweld the back boxes and refit the OEM ones i had chopped off and just add some tips to make it look good. because i would choose comfort over power anyday, not like i dont have any power being a 4.2 lol.

but thanks for that

aTOMic

Have you contacted MTM? They are not exactly amateurs in this field and probably have had some similar issues in other cars, if not in the A8.
I have experimented with exhausts on cars in the past and can attest to the fact that a tiny difference in pipe length, curvature, back pressure or even discharge angle can make a big difference in the sound in the car.
If you have a link to the system you have that would be interesting.
I frequently wish I could hear the BFM's wonderful sound better from within the car, but I guess this shows me to be careful what I wish for.
-Tom

mishar

Before you give up you may consider wrapping those with this, or similar.

bmwm750

Exactly. This is a common problem when playing with aftermarket exhausts. That said, MTM is no novice in this area, so I'd be very surprised that they would sell a system which didn't address cabin resonance.

MP4.2+6.0

So, is this the MTM exhaust specifically for your 4.2 (gas?) motor as a first question. And, was it new or used? I ask because MTM fitments are rare given the price, are available for a variety of motors including the TDI, and finally because as the car ages I expect some used ones might be around occasionally. The only other one I even remember on the board was an S8 system adaptation to a W12 about 5 years ago.

If you bought it new, did you consider their front section that is part of the larger cat back set up? I don't know their 4.2 one, but on the W12 set up, it seems like the cross over pipe is larger than the stock set up. On the W12 stock set up it hardly seems connected together (akin to a cross over) at the center resonator can. Similar on my old C5 4.2. As others have said more generally, you might want to get in touch with MTM for recommendations of what to do.

carterleeds

hi guys sorry for the late reply.

basically the exhaust are indeed second hand and was puchsed from a guy that had it on his a6, basically he did some work ect to it and then smashed it so broke the whole car.

so even though the car sound incredible the back boxes were not made for the car.

mishar i do have some of that bandage and was planing on using it, however i thought id ask first.

well i will wrap it and see how i get on if not, out with the new in with the old wich sounds naff tbh but nothing i can do unless i order a proper system however its very unlikely ill find one as you guys mention people like audi and MTM work with noise cancellation, i doubt exhaust "puter-togetherers" would do this especially in the uk as ive found a lot of them just to be welded and made not tested etc.