New Exhaust note????

[CStraface]

My truck seems to be making a new exhaust note. Seems to be running the same as far as vibrations and what not, and it seems to be making as much power, but I noticed that my exhaust sounds different. I just picked the truck up last night after sitting for a month (it was started every few days however). Truck sounded fine yesterday. But today something sounds different? When truck is missing... is there a noticable vibration or power loss? What else would cause a different sounding exhaust?