I have a 52plate astra gsi,over the past week my traction control light has been flashing if im on sweeping bends at 25mph and upwards,i believe the light flashing is the ESP ( think thats what its called ). it feels like the backend steps out slightly whenever the light comes on. Im looking for reasons why this is happening? the tyres are in ok condition.last week i changed the rear disks and pads,i also lowered it but removed it as didnt like the look, but everything was put back together correctly. the only thing i can think of is the caliper sticking?

You're ideas would be appreciated as i cant think of anything else it would be,sorry for the long winded explanation.