Apologies for reviving an ancient thread, but I just wanted to say that I wish I'd seen this a few weeks ago, before ordering a DS catback. The video of the system on the DS website makes it sound very subtle - both from inside the car and outside - and plenty of people on the STOC site were singing its praises.

So I was fairly gutted when I had it fitted and the droning started. It's fairly noisy at idle, but is really, REALLY bad when accelerating between 2000-3000rpm. I'm having to stick it in fifth gear on the motorway to keep the revs above 3000rpm, which is when the drone disappears. The mechanic at the garage where I had it fitted said he thought the drone would make him nauseous after a short while.

I'm having the exhaust taken off and sent back to DS next week for them to have a look at it. I was hoping I had a faulty one, but having seen this thread I'm now expecting them to say 'They all do this, sir'. Can't believe the time and money I'm spending on this to get it sorted!