Loud Engine Noise

[Rhort]

My car (52 plate Peugeot 406 2.0 petrol saloon) makes a loud noise; i.e the 'normal' engine sound increases in volume, but only between 2000 and 2500 RPM, or whenever the engine is braking (i.e. Run up to 70MPH and take my foot off the throttle, it makes the noise). Can anyone suggest what this is?

I'm thinking exhaust, but the way it's only at 2-2500RPM, or when engine braking is baffling me.

[heretohelp]

ide start by checking the oil level to rule that out.