Engine Rev / Rattling Noise? (Please someone help)

[TheKingSim0n]

For the past month or so I keep hearing like this odd rattling noise coming from like under the car as i accelerate the car. I also have some odd noise when the car is cold and I start it up for the first time in the morning, once it warms up it goes away but the rattling still is under the car. Its very annoying.

At first I was told by BMW around a few months back that my Catalytic Converter was going bad, I recently had it checked out by an indy, he says its 100% fine. I connected it to an ODB II and I get no codes for exhaust or engine (Thank G-d)

The rattling noise happens while in drive, park or neutral. no matter what I hear it. I checked out the Cats but they seem stiff and nothing seems to be rattling while its in drive I try and move them and their still in place, I hit em a little and nothing shakes, so it seems like there okay.....

What else can cause this? Can it be the O2 Sensors? :/

Thanks 4 the help!

[TheKingSim0n]

Anyone please? :/

[anerbe]

raise your car, grab a rubber mallet and start hitting things under the car. had a rattle under my wife's car - turned out to be a loose O2 sensor

[sfcl]

I really can't see what can be the cause of this rattle apart the cat, at least with the indication you gave. If the noise occurs only when the engine is running, vehicle stopped or not, and that nothing seems wrong when you move or hit the exhaust system, it couldn't be a broken exhaust braket. On the other hand, a worn cat doesn't always rattle when you hit it with something, sometimes this is only an internal part which is broken in the cat and only the gases or vibrations can make it rattling.

If the noise would occurs only when the véhicle is moving (and not vehicle stopped, engine running), I'd say that there are many other possible causes (transmission, loosen part somewhere, brakes, etc) however it seems that this is not the case.

[chilliwilli]

Aren't you the same guy with trany issues? If you're still driving your X without addressing the issue, don't be surprised if trany failure causes other components to fail...Your torque converter will suffer more damage as you continue to drive without addressing the issue.

[TheKingSim0n]

Originally Posted by sfcl

a worn cat doesn't always rattle when you hit it with something, sometimes this is only an internal part which is broken in the cat and only the gases or vibrations can make it rattling.

I was assuming it was internal since BMW told me that the cat was bad, I have not yet got a chance to replace it but If i were to replace it what do you think of the after market ones? Whats the best cheap price i can pay to replace the cats? And if I do replace the cats do I need to change the O2 sensors as well?

[TheKingSim0n]

Originally Posted by chilliwilli

Aren't you the same guy with trany issues? If you're still driving your X without addressing the issue, don't be surprised if trany failure causes other components to fail...Your torque converter will suffer more damage as you continue to drive without addressing the issue.

I do have tranny issues but its only a hard down shift here and there. When i drive past around an hour or two the tranny just gives in and i just keep getting high RPMs. I am going to get the transmission rebuild as soon as I can. I already have plans set for that.

Thanks for the helpful advice!

[shooter]

I have the exact same issue with my exhaust. I swear I have a leak, but everyone including the dealership says I don't. I only hear this noise when its started cold and when I get on it. When I get on it, it sounds like a air/rattle combo noise. Very hard to put in words. I can hear it best next to a wall, where it echoes. This is driving me insane!!!

[RPX5]

could be something as little as a loose heat shield! i had this dumb rattle and heard it the loudest when driving a parking garage, it drove me nuts forever! no one could diagnose, but then finally we found out it was a loose section of heat shield. very easy fix... just got some tin snips and cut the loose corner off.