help with boiler?

Hello, I really hope somebody can help me - tonight!!? My boiler is making a very loud noise - it sort of sounds like there is someone going past my house on a moped - but constantly!! Even when I switch the boiler down completely it still continues to make this noise! There is a leak coming from underneath the boiler and the pressure is far too high! I have read some things online just now........... but was wondering if there was anything I could do - i'm not desperate for the boiler to work right now - I just want to noise to stop!!??? Please help!!!??