My octy has started making a strange noise on startup. When I start the engine when its cold it makes a noise like the exhaust has a hole in it. This goes on for about 2 minutes then mysteriously stops! any idea what it is? It seems to be getting worse and now sounds like a tank on first start. Also I have a strange oil/temp light that has started coming on when its really cold. If i keep the engine running for a few minutes then swith it on and off again the light stays off!!!

the strange exhaust blowing noise is perfectly normal.it is the secondary air pump and should sound like that on start up.