E46 330i rattle under acceleration

[petrolveins]

Hi chaps,

I've had my 330i for about 8 months now, and in the last few months I've noticed that under load, either gentle or hard acceleration it often makes a rattling noise from underneath, like a tin can rattling against another. It could have been there since day one but I've only noticed it with the windows down. I'm fairly sure it's from under the car and not from the engine. It only makes the noise under load, and at any point randomly in the rev-range, though at high revs the engine/exhaust is too loud to hear it. It is aggravated by driving up steep hills. My mechanic has had a look, I replicated the noise on the test drive with him, and he wasn't sure but suggested it could be heat shield, so he had a look underneath and everything was fine. Other people have suggest the Cats could be the cause or even a leaking diff. Anyone come across this before? The car other than that is fine, the noise just gets on my nerves and isn't a fitting noise for a car of this nature to be making.

Any help greatly appreciated.

[essexplumber]

Catalytic Converter? Does it feel like its lost power or using more fuel than normal? Had a similar thing on my E36 318is years ago, sounded like a bag of spanners under load. A family freind changed it at cost (he owned a mechanics franchise) but it went again, he said it may have been a dodgy batch as the second on went too.

I asked if it could be a fault with the air/fuel mix burning the Cat out, he then traced it to a faulty air sensor IIRC.

[petrolveins]

essexplumber said:

Catalytic Converter? Does it feel like its lost power or using more fuel than normal? Had a similar thing on my E36 318is years ago, sounded like a bag of spanners under load. A family freind changed it at cost (he owned a mechanics franchise) but it went again, he said it may have been a dodgy batch as the second on went too.

I asked if it could be a fault with the air/fuel mix burning the Cat out, he then traced it to a faulty air sensor IIRC.

I don't think so, still feels very quick and has always averaged around 22mpg, and 30+ on longer runs. How can I check if the cat is at fault?

[essexplumber]

petrolveins said:

essexplumber said:

Catalytic Converter? Does it feel like its lost power or using more fuel than normal? Had a similar thing on my E36 318is years ago, sounded like a bag of spanners under load. A family freind changed it at cost (he owned a mechanics franchise) but it went again, he said it may have been a dodgy batch as the second on went too.

I asked if it could be a fault with the air/fuel mix burning the Cat out, he then traced it to a faulty air sensor IIRC.

I don't think so, still feels very quick and has always averaged around 22mpg, and 30+ on longer runs. How can I check if the cat is at fault?

Does it smell a bit "rich" from the exhaust? I'm no mechanic just going on experience but it sound like the Cat to me.

[steve_bmw]

Pinking? Mine makes a rattle sound when I put my foot down when it's hot, If I use super unleaded it goes away.

[4rephill]

Heat shield resting on the prop-shaft at the gearbox end?
(Quite a popular fault on e36's and e46's)


(I know you say your mechanic has had a look but it may have been missed!)

[SBN]

My e90 rattles when rolling but at a stand still it makes no noises just the sweet sound of the straight 6.

If it is the CAT wouldnt it rattle all the time...?

[essexplumber]

SBN said:

My e90 rattles when rolling but at a stand still it makes no noises just the sweet sound of the straight 6.

If it is the CAT wouldnt it rattle all the time...?

I'd have thought the more pressure and higher flow of gases would increase the noise. My moneys on the Cat.

[petrolveins]

Cheers guys I've just put half a tank of normal Shell in there, but when that runs out I'll stick in some super unleaded. It's getting the brakes done soon, so I'll get that heat shield looked at then. But it doesn't smell like it's running rich at all.

[SBN]

Sorry if at a stand still and I rev it there is no rattle. Only when driving around built up areas I can hear the rattle with the windows open not when closed. Normally the sound happens when at 20 and then accelerate for a few seconds then disappears so it only happens at certain revs and when moving.

Could it be the exhaust valve,

[steve_bmw]

I'll put money on its pinking, put some super in it, give it a run to adjust mixture/timing and see if it goes away!

[JimexPL]

steve_bmw said:

I'll put money on its pinking, put some super in it, give it a run to adjust mixture/timing and see if it goes away!

I'd expect it to be the DISA or a heat shield.

Un plug the DISA and go for a drive to see if the noise has gone, 5 minutes and c.£125 to replace, and any mechanic should be able to diagnose a rattly heat shield.

[steve_bmw]

would you hear a DISA when driving?

[petrolveins]

Ummmm DISA???

[SBN]

Yeah disa? What's that please?

[c123]

Is it a metallic rattling, only around 1500rpm when the car is moving (not possible to recreate it when revving it at a standstill)? If so I’m willing to bet it is one of the brackets that holds the exhaust. Which is a cheap fix!

I had those symptoms on my e39 and it turned out to be a crack in the bracket where one of the nuts connected to the bellhousing. Even thumping the exhaust on my back it was very difficult to find as the movement was so slight. I presume at 1500rpm, under load, the torque starts to move the exhaust enough to get the bracket to resonate.

The e46 has different exhaust hangers but it looks like one of them mounts to the gearbox. Get under the car and thump the exhaust and check these bit for movement manual box or auto.

[steve_bmw]

Good call on that exhaust bracket, it's certainly something that could be overlooked.
The disa is a valve fixed onto the inlet manifold, black box above throttle body, can rattle when shaft is worn, possible but it would have to be very worn to hear it when driving.

[CarbonM5]

Exhaust clamp forward of the cats probably,the bolt rusts off and let's them rattle around.

[Thomostash]

Possible Vanos issue?

[steve_bmw]

Thomostash said:

Possible Vanos issue?

Not on an m54.