3.9i cat tapping when warm

Hi i have a 1994 v8i disco when its warmed up the right hand cat starts to make a tapping noise quite loud its getting on my nerves question is is it the cat no good any more or could it be that the engine is not running right and causing this to happen has any one any thoughts on this thanks

when cold tap cat with hand-see if it rattles

Cheers will do in morning its still warm at moment

Hi been under it today and it seems solid hit it hard with my hand,so it making me think it could be engine not running right,ive changed plugs leads dizzy cap and rotary arm air filter but couldnt do fuel filter as nuts too tight job for another day

could be an exhaust leak or a sticky tappet

Hi I know it's the cat tapping as had my ear against it think I try a new one and see thanks