Original owner of my Brab, Mr J500ANT, said he used to use 95 RON standard petrol and there's certainly been no long-term effects, but when I once had to put £10 in of standard (during the last idiots' panic-buying session) there was a noticeable knock and lack of oomph, so I always use Shell V-Power. Used Tesco for a short while last winter, but had about 20% less MPG and the car just didn't like to move.
I have a rattle from my parcel shelf too, I believe it to be the flap that hangs over as it doesn't seem to rattle when the flap is folded on top of itself.
The rear roof blind is also snapped at one end, and that can rattle on a bumpy road, perhaps yours is also damaged, or loose.