your wheel nuts or if you already do well done i need to start doing it ALOT more, coming back from college there heard this grinding sound first thought was my c.v joint as it is shagged bout 5 mins away from my home my wheel came off well half off came to a sudden stop with a loud grinding sound i was thinking oh god this has caused alot of damage. was very very lucky and no damage was casued just the inside of my wheel is scraped of the disc but thats nothing. keep thinking if i was on the motor way doing 100 or so what would of happend.