Strange Noise in 1st/2nd gear

[brucemillar]

C55 AMG estate

Last week I noticed a "rattle" starting on my car if I lift off in 1st or 2nd gear.

By yesterday it had got a lot worse (louder) and sounds like the exhaust. It only does this when the car is really hot (after a run) and when the noise starts you can hear it in Park or Neutral if you blip the throttle.

From the outside it sounds like it is coming from the middle of the car/back end of gear box. This makes me think cats or resonator?

However, what does worry me is that it only starts if I use the car in Manual mode. i.e. If I change gear with the buttons or the lever. It does not do it if I leave it in auto. This may well be coincidental. Could using the the car in manual induce a rattle from the gear box that continues in Park and Neutral?

FYI. The noise sounds like something hitting the prop-shaft but it can't be that as it continues when stationary.

Bruce

 

[BlackC55]

It will probably be a broken up CAT.

Time for a de-cat methinks.....

 

[NW_Merc]

Would that affect emissions Olly, if say it were done on a 4 cylinder car as opposed to a V8?

 

[brucemillar]

Olly

I plan to take off the secondary cats and resonator. Any ideas why manual changing seems to trigger the rattle?

 

[BlackC55]

Would that affect emissions Olly, if say it were done on a 4 cylinder car as opposed to a V8?

On a 4cyl it is likely to fail the MOT. A V8 C55 has 4 cats.

 

[BlackC55]

Olly

I plan to take off the secondary cats and resonator. Any ideas why manual changing seems to trigger the rattle?

No idea. Before doing anything get it on a lif and have a poke about. They also suffer with the parking brake cable rubbing on the prop.

 

[brucemillar]

Olly

Parking brake sounds good to me. I will let you know.

Many thanks

Bruce

 

[brucemillar]

Olly

Spot on. It was/is the secondary cat on the passenger side rattling like a bag of gravel in the exhaust. Off for de-cat and resonator removal. How much would you charge for that?