W212 E220 Knocking/rattling noise when crawling

[andip]

Hi, I'm hoping someone can point me in the right direction/provide some advice. Driving back from work in my 2014 E220 Bluetech (96k miles) on the M40 traffic caused me to come to a standstill. When I got to crawling speed in Gear 2, sub 1mph, and keeping pressure on the brake, a knocking sound occurred which feels like it's coming from under the drivers seat/centre console. Since then, it's been happening every time I slow the car down to crawl slowly in traffic. It's fine under acceleration, or when stopping, but noticeable when I suppose the second gear is on the brink of changing down a gear or stopping. Any ideas what it could be? All the brakes look fine, engine oil good, and noise/issue at any other time.

 

[andip]

All resolved, turned out it was loose exhaust clamp, where the bolt had broken apart. image shows temp fix for the clamp.