constant "ing" from my exhaust muffler

I have a constant "ing" sound from my the rear of my 96 CAMARO. It's not loud, but if you stand near to the rear of the car, you can hear it quite clearly. On closer examination, it seems to be coming from my exhaust pipe/muffler. My car still runs pretty well though, and there is no usual o/p from the exhaust.

Can it be due to choked valve, or other reasons?
PLEASE HELP. tHANKS.

my camaro done this, but mine the passenger
side exhaust hanger was bad and it would vibrate and make a pinging noise

lemme know if u get anywhere with this one. mine does the same exact thing, and i haven't found someone yet who can help me at all.