Scraping/grinding/rattling on engine braking

[Wheelyboy]

Hi all I've checked your forum out a good few times in the past 3 and a half years and found plenty of tips to help keep my DS3s sorted - thank you.
I'm a driving instructor on my second DS3 (first one was a Cabrio) and I've always had PSA cars (Peugeot 307/206/207/208) over the years but never had this particular irritation.
I now have an ongoing problem which Citroen either cannot identify/do not care to solve and of course when I get a technician to test drive the car the noise isn't there.
Once the car is up to temperature I frequently get a scraping/grinding/rubbing noise mainly on engine braking using 2nd gear from 25mph down.
The same thing happens using 3rd and 4th gears and whilst not so noisy it's still irritating. It can also happen when accelerating.
Some of my pupils hear the sound from the transmission tunnel and I sometimes think it sounds like an off balance fan spinning and the noise appears to come through the driver side a/c vent - anybody got any ideas?
Citroen have had the car back twice but tell me there is nothing wrong or unsafe about it and they can find no evidence of rubbing - hmmmm.
All my cars have been fitted with dual controls and all have suffered with rattling clutches when manoeuvring slowly but I've yet to have a clutch fail and my cars get 30k+ miles pa heavy duty usage. Current car has done 49k.
MPG not affected as I get 53-55 which is similar to my previous cars fitted with the same engine.
Would much appreciate any advice or conformation of similar problems and a cure.
Thanks.

[BenS]

Although it doesn't fit all the symptoms the first things I think of are sticking brakes or a stone caught in them.

The noise from fans though might be something though, as there are floor fans either side of the gear lever and that could account for the sound from there. Do you have A/C on while this noise happens? If you turn the fans off completely do you still get the noise? Just trying to rule out where it could be coming from.

[Wheelyboy]

Thanks for your reply Ben.
The car had a 48k service 2 weeks ago so brakes thoroughly checked over and no foreign objects found.
The scraping noise still happens with the fan off.
I think the off balance fan description I gave came to me because the radiator was replaced a few months back (holed) and it occurred to me that maybe refitted fan was off balance.
In retrospect the scraping noise was there before rad was replaced.

[WTF]

Welcome Hope we can solve this for you!

I have an unidentifiable noise,so I know how frustrating they can be!

[Dsdennis]

It could be broken rubber attachment on air filter box - it can make noises when engine braking

[Andy ADI]

Hi all had the same problem also driving instructor dealership said it was the air box come lose as Dsdennis said, mechanic said it’s from pupil bring clutch up quickly and jerking engine or similar.