[v8fan]

When cold starting the overall impression I'm getting from my M5 is that its rather noisy - perhaps the first 5 minutes or so.

As soon as the temperature rises then noise level drops considerably.

I realize that the idle rpm's are higher when cold, but I'm referring to the noise level when driving. There quite a lot of resonance from the exhaust, and the overall exhaust sound level is quite high. I should mention that the car is completely stock.

I'm not talking about the great sound when the engine is hot and pushed from a little bit to a lot

I read somewhere that the engine management, in order to heat up the cats, makes the car somewhat rough until the temperature is above a certain level.

I'm just wondering if I should start looking for reasons, or if this is just the nature of the car.

Please tell me your experiences.

PS: I have only driven the car in subzero or close (Celsius) temperatures.

 

[russap5]

Are you referring to the secondary air pump noise at cold starts?

If you're not sure, it is located in the passenger wheel well and can sound like a jet engine when it is wearing out.

 

["S62"]

Cats???

 

[993 4S]

I used to have a really loud rattle inside the cabin on cold-starts that went away as the car warmed up. I couldn't hear the noise when standing outside the car or from the engine bay, so I determined it wasn't VANOS-related.

Turned out part of the exhaust was loose. When cold, it would rattle like crazy--sounded like you were shaking a bunch of marbles in a box--and as the car warmed up, the metal expanded and the sound went away. Quick exhaust adjustment took care of the problem. May be worth checking.

 

[E55AMG2]

What he's referring to is the fact that the car is louder on cold start. It's completely normal to have that kind or resonnance until the Ktemp rises to 40C or so

 

[MrCrashRR]

Are you referring to the secondary air pump noise at cold starts?

If you're not sure, it is located in the passenger wheel well and can sound like a jet engine when it is wearing out.

That's what it sounds like to me too. It comes on during cold starts for about 2 mins or less, IICR and it can be very loud.

The one in the picture is upside down, but in the correct location. So If you want to go check it out on the next start, and just wait a about 2 mins for it to turn off, and see if thats where its comming from.

 

[v8fan]

I think I'll go for the explanation offered by E55AMG2 since the sounds are the normal ones, just a lot louder.
I can hear the secondary air pump noise, but that's not the culprit.

I think I'll check the exhaust and its mountings, if this checks out I'll just leave at that

 

[E55AMG2]

I think I'll go for the explanation offered by E55AMG2 since the sounds are the normal ones, just a lot louder.
I can hear the secondary air pump noise, but that's not the culprit.

I think I'll check the exhaust and its mountings, if this checks out I'll just leave at that

I wouldnt bother unless you hear racecar level noises till the car warms up.

 

[v8fan]

I finally figured out what was cause of the high noise level.

It turned out to be very simple - the two rubber O-shaped exhaust mounts had lost most of their effect, strangely enough the effects of this wore off as soon as the exhaust became hot.

The sound was not metal to metal but as the O-shapes had gone completely flat, it was rubber to rubber making a booming sound.

After a change of these two mounts the noise levels are perfect