Instant metal knocking noise from engine dept when taking foot of the accelarator slowing down with low gears engaged 123 on a RENAULT laguna 2003 1.8 petrol please help?

I had the same noise, but in diesel one, the problem was in rubber between engine and frame where engine bolted down.actually engine wasnot bolted down tight enough, that's way when i pressed accelerator it was noise. engine just shakes against the frame.