[mike07s]

I've just fitted a set of AR Design catless downpipes, on occasion (above 4000rpm) I can hear a loud hissing sound, definitely sounds like some sort of boost leak however the car isn't displaying any physical symptoms. I've experienced boost leaks on my previous car and it sounds awfully familiar. The issue is I didn't hear any sounds like this pre-install, having searched about I've not found any similar stories. Does anyone know what could be causing it and if there is a method for checking it?

To expand if I rev up to 2000rpm when parked I can hear the boost being recirculated not hissing out like it is leaking. The exhaust also doesn't sound great when this happens at about 4000rpm, the closest description I can think of is one of those party horns with the paper bit ripped off.

Sorry in advance for the fairly vague description but after 100 miles + of driving I'm no closer to working out what it is.

[idnan]

I have had this issue come up when switching to the ISO version of JB4. It appears it relates to the position of the wastegates on part throttle. With the catless DPs, the noise is not masked and can be heard in the car:

http://www.e90post.com/forums/showthread.php?t=622021

It could also possibly be loose/leaking v band clamps joining the downpipes to the turbos.

[mike07s]

Originally Posted by idnan

I have had this issue come up when switching to the ISO version of JB4. It appears it relates to the position of the wastegates on part throttle. With the catless DPs, the noise is not masked and can be heard in the car:

http://www.e90post.com/forums/showthread.php?t=622021

It could also possibly be loose/leaking v band clamps joining the downpipes to the turbos.

Thanks for the info Idnan, after reading that thread I think I'll give it a few weeks then look into replacing the V band clamps, seals and gaskets.