With a single resonator and 3" pipe, I got pretty bad drone in the cabin at highway cruise speed. added a second can, and it helped a little. Mufflers are morosso spiral flow.
excuse the whirr, its the fan on the inverter
You can see how it's peakey at 250HZ
In the clip I get off the highway, sit at a light for a minute, and run through 3rd.