It is now agreed by all at the track that the Red Bull car definitely sounds as though it is blowing off-throttle – something that was specifically banned.
They must think they have found a loophole in the regulations, and can somehow keep the exhaust blowing while off the throttle, thus increasing their downforce and making the car go faster.
If any random bod can judge this by hearing it, why are the FIA not doing anything about it? Even if it is fine, they can investigate it and it would then be confirmed as legal.
But either way the FIA is there to clarify such matters, and as of now they are not doing that.
From other news of Silverstone qualifying, the McLaren car is not as strong on the intermediate tyres and is making it very difficult for drivers to get heat into their tyres.