is it more of a buzzing sound or a rattling sound? mine is usally around 1700 to 2500 rpms and it's from the heatsheild around the cat that rattles like crazy. kinda sounds like a buzz from the light gauge aluminum rattling. but like you said it, you've noticed since you got your tune so it might be something else
I couldn't tell you what side it is comming from. I don't think its the heat sheild on the cat becuase it stops after about 4 seconds. I am thinking about tuning it back to stock and seeing if it makes that noise.