Like I stated. It just started last night. I have 4200 miles on it and its a m5 06 tC. When I start the car there is a single knock which sounds like it is coming from the driver side. The only mod I have under the hood is an injen CAI. I turned the car on and off 4 times, driving around the block in between each. And each time I turned it on, I believe the sound was quiter each time.

Any ideas?

 

I've got the same problem. I disconnected the lower portion of the CAI from upper portion, started it, and there was no knock. Also when it rains/is damp out, the knock is replaced by a rubber on rubber "squeak" noise. This leads me to believe it may be something related to the vibramount located below (where you had to relocate the ground). I'm thinking the tube down there or the filter is hitting something due to the engine torquing

 

Thats what my first guess was (the CAI). But if thats true Im trying to figure out why is it happening now? I have had the intake on for around 300 miles. And this is the first time I have heard this noise. By the way I went out to listen to the noise again and it sounds more like plastic thudding then metal.

 

Im probably just going to have to dive into the CAI tomorrow unless someone can come up with another good lead.

 

im pretty sure this happens, because when the engine is very cold, it will shake much more initially then when it is very warm. The knocking you are hearing is the lower arm of the intake banging against the fender

nothing really to worry about

 

The CAI bracket near the battery breaks often. Check that.

 

So it appears everyone is banking on there being a problem with the CAI. Im going to work on it when I get off of work. Hopefully it is something small and simple.

Thanks everyone

 

You sure its not the Antilock-Brake test knock that you're hearing? That usually also makes a single knocking sound every time you start driving.

 

So once I popped the hood and took a look at the vibrant mount near the battery of the CAI the first thing I noticed is the bolt rattled completely off. I replaced it with a 6M - (1,0)mm flange nut and the rattling stopped. Now I need to figure out a way to keep that bolt from rattling loose again. It was only on there for 300 miles.

 

try getting a lock nut... they work wonders...

 

Thanks. I'm going to pick one up tomorrow.

 

not a problem... and another thing i thought of last night at like 3 am but was too lazy to walk to the computer was make sure you have that rubber lining going around the hole in your fender for second piece of your CAI sometimes that'll do it too and for future reference you might want to invest in a torque damper because the bracket may not last too long without it... just an idea, snapped mine the other day because i didn't have my damper on yet i knew i should of got off my lazy **** and installed it lol

 

I was looking into a torque dampner but I was under the impression that if you have a front strut bar (I have TRD) that the dampner can't be installed. Do you know if this is true?

 

well i'll tell you what... my dc sports bar should be here in a day or so and whenever the damper gets in to ZPI i'll have it in like another two to three days... i think i should be able to let you know within two weeks... i don't see it being a problem... the damper would have to go on top of the bar and might be a tight fit... guess i'll be your guinea pig lol

 

Ha. Sweet deal. Yeah you are going to have to let me know how that goes. If you can get both the strut bar and the torque dampner on there I'd be stoked and definitely up for picking one up. Thanks for your help so far. Keep in touch.

 

Torque Dempener + Strut Bar works fine:

 

Oh sweet.... I'm going to have to look into picking one up now

 

I had my bracket break and took it in. The dealer had to replace the motor mount because that's where the bracket was welded to but I got it covered under warranty. ETD for sure will help! I'm getting one.