With air, as it's under high pressure - if in doubt worry a bit, but safety features do exist in cylinders.
It's normal for a depressurised cylinder to rattle - eg at the fill nipple. But we cannot say from a description what the issue is
Idealy, depressurise and have it looked at by someone' competent' (not just a bloke who has filled in the past)
If you have access to a remote line, connect up but not to a marker, open the slide check if applicable, slowly screw down the ASA on the regulator and allow the air to purge. When it stops screw down some more
If you do not have a remote then you can use your gun - preferably disconnect the macro line so if does not feed air to the gun, if you have an on/off ASA then switch on and slowly screw the cylinder into the ASA