06 avalanche exhaust clunk

I have an 06 avalanche  that just started making a
clunking noise  appears to be coming from the
exhaust between the manifold and resinator or
catalytic converter . When i give it a little gas the
noise stops then starts back up when it returns to
an idle. Any odeas on what it may be ?  Thought
maybe a broken 02sensor but the dummy light isnt
on maybe the internals of the cat. Or resinator  are
loose?