Over the last couple of days, i've noticed that the roadnoise from the rear of the car is becoming louder. I've fitted some ST170 wheels to my 2003 Focus Zetec a few months ago - when i fitted them, the road noise was noticably louder from the tyres bigger wheels and tyres, but over the last couple of days, the rears seem to have increased in road noise again, like when i fitted the ST170 wheels.
Could this be the wheel bearing(s) or maybe the tyres?? And if it is the rear bearings would it be becuase i've put the St170 wheels on causing more wear?

Also, twice today, there was a weird metallic scraping noise coming from the rear, like something was hanging off the car and scraping on the road, but only lasted for a few seconds whilst in 1st gear pulling away.
I've looked underneath but theres nothing hanging off or missing...i'm totally stumped!
I might try swapping the front wheels with the back ones and check the rears for play or movement tomorrow, but has anyone else had this?

The scraping noise didn't sound too healthy! - possiblkr bearing failure maybe?