I have a TSL stainless steel open neck downpipe and centre section fitted to my newage WRX and have noticed that since it was fitted the turbo whistle is a lot louder (as well as a tinny sound when the car is cold). I am fairly sure that this is normal due to the removal of the CATs which I presume would deaden the noise somewhat and also the fact that the downpipe has a larger inlet from the turbo, but could someone confirm that they have also noticed this.
This does not have a detrimental effect on the car at all and is purely an observation.

Cheers

Andy

 

A decat downpipe will not deaden sounds as much, so turbo spool is more noticeable!