Knocking noise from Renault Scenic

[Darth]

I have a Scenic 1.6 Sport which has developed a knocking noise at the rear which also sounds under the car. It seems to happen when I have just set out on a journey at around 2 miles. It is just a single knock, witch does happen at other times but not very often. I thought it could be due to the rear brakes binding and the calipers releasing that was the cause. I had the rear brake pads and discs replaced, as the discs were badly scored anyway, but the knock is still there. The front pads were replaced at the start of the year but the discs weren't, I am thinking of replacing them soon. I have also wondered if it could be the cat, as on a couple of occasions the individual coils on two of the plug have failed resulting in the engine miss firing and unspent fuel going in to the cat, although the mileage done when this happened was at most 10 miles on each occasion to the dealer. The car has done 47000 miles.

[larsen_huw]

Gosh.

That's a lot of stuff to go wrong on 1 car ..... I'm glad i don't drive a Renault.

Firstly, the spent fuel may well have knackered your cat, but there's no way that's causing the knocking.

The 2 most likely causes are that one of your rear suspension bolts isn't done up correctly or your exhaust is fouling on something.

Does the knock happen at a particular point on your regular journey, say during a high speed corner, or a tight roundabout?

Keep an ear out for it, and see if there's a pattern to when it appears (say, only when turning sharp right at over 25mph or whatever).

[Darth]

It usually happens within the first couple of miles, one knock and thats it. Which makes me think brake callipers slow to release, if this is possible.

[larsen_huw]

Darth,

Many things on a car are possible.

And without seeing for myself, it's very difficult to rule things out.

However, i would think it's highly unlikely that it's the brakes. I'm not saying it isn't, just that there are several more likely culprits i would look at before turning my attention to the brakes.

Does the car feel sluggish before the knock (similar to driving off with the handbrake on), then more sprightly after (as if the handbrake had been taken off)?

[Darth]

hard to say, but it probably is just a little bit sluggish. I was wondering if it could be the back box on the exhaust :naughty: . I am going to get the exhaust checked out at on of the many kwik fit type places in the next few days. the car handling itself is just a good as ever, and for a car of its type quite responsive.......pity about that single knock when warming up. :)