performance Muffler / flowmaster..?

[Maluco]

I had a cheap flowmaster type muffler installed a while back and it sounds like something is wrong with it. At 2500 to 3200 RPMs I get this low and loud hum and it sounds like it's coming from the back or muffler. I guess that's only logical since that's where the exhaust/sound leaves the car. I am going to get it looked at this weekend. Any ideas on the noise?

My main question is if I decide to replace that piece of sh** muffler, what kind of muffler / flowmaster should I use. I don't really want too much of a sporty sound but something low and not that loud would be fine. (the one I have used to sound great but I don't know what is causing it to be so low and loud now) It even seems like there's some vibration....

[Budget Beater]

thats resonance. i would recommend running magnaflow muffler, they are only like $50-60 and they are a true free flow perforated core design for maximum HP and you may want to get a better resonator as well. if resonance can get bad enough it can cause big vibrations. it may be a good time to just replace majority of hte exhaust system with a single 2.5" system for cheap. you can get 2.5" cat for $35, and resonator for about $20 off ebay. Magnaflow muffler for about $50-60 from www.justmagnaflow.com . you can do the whole system including piping for probably arond $200 installed. just a suggestion, no point in replacing when u can upgrade :)