Originally Posted by yellowhammer

Ok this is what I did after removing stock muffler and installing a Magnaflow muffler. Really liked the new sound of the Magnaflow but the drone between 2100 and 2800 RPM,s was really bad
and drove me crazy. After researching a Helmholtz Resonator on a Nissan forum I found the formula for a 1/4 wave resonator they also tried X pipes with no luck. With this formula I was able to target this RPM range and the frequency in Hz of the drone sound at 200 degrees exhaust temp. I had a J pipe or branch resonator made to this specific length and welded into the exhaust before the muffler.
WOW could not believe the difference, it starts at about 2000 RPM,s at 2500 RPM,s you can hardly hear the exhaust at all totally dead, around 2900 RPM,s the drone is gone and you can really hear the exhaust, sounds really good. What it does is bounce a 1/4 wave back into the exhaust at that RPM and cancels that specific frequency really works well !!!!!
PM me if you want the details of the formula and my specific build.