What is the grinding/rattling noise at low RPM?

[ShockDiamond]

I've wondered for a long time now what the grinding/rattling noise is at low RPM when Formula 1 cars are decelerating. David Coulthard began to explain it during a Grand Prix part way though the 2011 season, but he was interrupted and never finished his thought.

If anyone can provide the answer, I would aprpeciate it. Thanks.

[wesley123]

Well 90% of the forum currently goes about it.

These are the blown diffusers, when not on throttle they 'blow' the exhaust so it delivers continuing exhaust flow, this creates the sound you describe

[ShockDiamond]

That's awesome - thank you so much for replying. I knew they used blown diffusers but I had no idea they made that noise. I'll have to read up on it. Thanks again!