I know alta CAI is the loudest one out there. Because Alta instructed that the firewall should be removed while M7 installation still has the firewall so you will not hear the throttle whistle. IMO, Alta CAI is more noisy but is more effective, with larger intake box volume, the engine will breath easier. Also, alta CAI is cheaper, i got it for $170 shipped. M7 is $250 w/o shipping. If you go with alta but do not want the whistle, you can try Burley solution although when you decide to go back to stock your firewall will have holes on it.

 

@burley. Do you have the chance to get a pic of that custom firewall of yours?
If you can post it I will appreciate it.

 

Will do tomorrow.

 

thanks alot burley

 

So here are the pix of the holes I drilled into the firewall. Its helped cut the noise quite a bit, but as the weather warmed up, I notice that the sound is much louder with the windows down. I think the key is really the stock air box.

 

thx burley, definitely will try that one out when i cant stand the noise anymore. another way to keep the noise down on the hwy is driving at speed limit. if i cruise at 65 no noise 70 sm whitsle noise every a few seconds or so 80 lots of whistle noise 90 noise gets louder but still annoying 100+ (the best cause its the 2nd pitch sound which is the SC whine not the kettle noise)

 

Some cars whistle, and others don't. Only sure-fire fix for a whistling car is either (a) go back to stock airbox or (b) JCW airbox - neither of which eliminate the whistle - they just muffle it so it isn't nearly as pronounced.

My saga:
http://www.blimeycabrio.com/?p=138