Yeah, see I can't tell which sound OP is referring too - or maybe both? Certainly the other sound bothers me more as its more of a thud sound which implies mass behind something doing something it shouldn't - but when he revs it it sounds like when I forgot to torque down the 14mm bolts on my OBX header when I installed it on my 97 SE-R, I got in the car to start it up and didn't notice anything until I hit the gas and you hear the spspspspspspspspspspspsp sound