There's a great deal of squealing from the passenger side of the car when i slow it down and change gear. It disappears not long after changing gear and speeding up again, especially in higher gears, and isn't affected by braking. It seems to have started quickly - the car hasn't been used much by me or the previous owner until today and it was fine on a test drive and this morning but appeared this evening. Could it be gearbox oil or something else?