Hi, 
  
New to posting so hope ive done this right. 
Can't find anything about this problem but I am searching on an iphone. 
  
I have the cobra back box and mid pipe fitted. Today i had the stillen y pipe fitted but the exhaust is knocking. 
  
I am abit suspicious of the work quality from my local garage as they fitted the cobra backbox wonky. 
  
Should the cobra back box + mid pipe and stillen y pipe fit with no issues? (Oem cats) 
  
Thanks 
  
Jason