My guess would be the throwout bearing may be rattling a bit or a loose downpipe mount bolt or heat sheild bolt since its happening during decel. Ive done 2 clutch jobs on my 02 and the dumb thowout bearing clips never stay on right so most people dont use em and it causes the t/o bearing to make a lil noise. As long as your clutch is engaging fine, Id roll with it. The t/o bearing may wear out a lil early. The rattle always comes back. You could try the tsk kit that replaces the flawed stock setup.