Hydraulic suspension warning lights flashing & bang/ hiss

[pld118]

Dont know if this is correct section.

Had 4 new tyres fitted on my Q7 this afternoon. Got home and after switching engine off there was like a generator sound coming from under front of car (to the inside of the front driver's side wheel). Then there was a loud bang, some smoke/ or steam came from under car, the generator sound continued for 20 minutes. After the bang there were many tiny little round cream coloured pellets all over the drive and when I started the car, there was a loud but brief angry sounding hiss from under car and when I drove it off drive the hydraulic suspension warning lights started flashing and the front end of the car lowered, the front arches coming to rest just over the front wheels. Every time I open driver door and/or start the car, the hiss sound happens...

Does anyone recognise symptoms please/ does anyone know what exactly might have gone on?

The car is under warranty but could the tyres fitters have done something wrong?