I noticed the other day that my pypes pype bomb exhaust makes a groaning noise if I'm in a certain gear at low rpms... Especially 2nd... It almost sounds like it's vibrating against something or something is loose but I just checked under it yesterday and everything is tight. It doesn't seem to do it when I first take the car out, but it seems when it heats up, it does it... Anyone know if this is normal or if it will go away?? They are pretty new exhausts...