Previous owner had custom 2.5" exhaust w/ Thermal R&D muffler put on. A couple weeks later he backed into a curb and the muffler took the full impact. It bent the exhaust in several places so he took it to a shop (non-performance-oriented) and they fixed the bends and patched a leak near the header (must've been quite an impact).

Well anyway, the car is in my hands now and I'm half embarrassed to drive it with the way it sounds. At around 2.3k RPM's it starts to develop the "rice" tone (weed wacker) but gets drown out once it reaches into the mid 3k RPM range. It sounds fairly good (deep/throaty) aside from what I now call the "rice eruptions", where it sounds like it's trying to spit something out. I'm wondering if the previous owner's little accident caused a leak that is making the noise.. or if something is going on internally (in the engine) between 2.3k and 3k RPMs that's making the the exhaust note change. Any input?

 

Really about the only thing you can do is have it redone. Don't patch, previous owner already proved that didn't work.

 

When you change the capacity/shape/length of an exhaust (or any kind of tubing that flows air), you will change the tone. This is the basic principle of how brass instruments can play different notes by changing the length of the pipes through which the air--and vibrations (more on that later)--flows.

The reason, however, that it is making a ****-ton of noise at a specific RPM range is because of resonance. When you flow air through a pipe at a constant rate, it won't make any noise (or so little it won't really be noticed). When you flow exhaust, though, it is not at a constant rate. The air is transmitted through the exhaust in "pulses" because there is always a gap in time between cylinders firing. This creates noise through vibration. When the frequency of pulses gets higher, as RPMs increase, the exhaust pitch changes. Once you reach a certain RPM, the pitch of your exhaust will vibrate to the point where the frequency creates harmonic resonance in the entire chassis of the car--or at least enough of the car to notice. When you pass that frequency on acceleration, you'll cease to hear the noise caused by resonance.

Long story short, to get rid of it, you need to modify your exhaust length, shape, or volume. The only thing to be wary of, though, is that you might still get the same kind of resonance through your car chassis but at a different RPM.

Make sense? I'm lousy when it comes to explaining things sometimes.