Exhaust Problem HELP!!

WIERD PROBLEM. My exhaust sounded fine until today; where there is a wierd STUTTERING exhaust note coming from it. I would rev the car to 2.5 rpm, and the needle would sort of stay there with the stuttering exhaust note getting louder. Then, it would break through the 2.5 barrier with the rpm going up and the exhaust would sound fine from there on. But everytime i change gear, the barrier and the stuttering would be there again. Is this BACK PRESSURE?? What could be wrong??? I lose power when there is the stutter and could hardly climb up the slope to my house. PLease HELP!

P.S: What exhaust system is recommended for power gains and a nice, deep but NOT LOUD TONE. THANKS ALL!

i think im gonna go for the flowmaster 60 series. IT has a name and sound you can trust. Here is the link for some video clips they have with their exhaust on a type r http://www.flowmastermufflers.com/web10/SePerfMuff7.html

I was thinking more along the lines of the APEXI N1 or the APEXI WORLD SPORT? What kind of power gains am i lookin at? And what bout the EXHAUST SOUND? THanks all.