rattle help

i have a 99 disco td5 auto. i noticed the car running rough on idle and developed a rattle[sounds a bit like the exhaust baffles rattling. i had a look underneath and there is a rectangulaer type shape next to the handbrake drum with a bolt going through it. thes seems loose and the cause of the rattle. i have looked everywhere to find out what this part is and cannot find it. i want to know if there is a rubber that could have perished or if it needs udjusting or replacing. sorry to be so vague i just dont know what else to call it. many thanks neil

after jacking the car up. i realised it was a mounting doh!! i have tightened it up and all is good again