As DW335 has been mentioned a few times with its different exhaust arrangement and slightly different sound, I emailed Arriva London to ask what had been done to it.
Thank you for your e-mail.
Our engineering technical team have advised that DW 335 is one of a number of buses from several operators being used by TfL to trail exhaust system upgrades. The unit on this bus is manufactured by Baumot.
The engine remains the standard type fitted to the “Mk2” DW-type.