When I'm using engine breaking to slow down, and I touch the rear brake pedal, I often hear a weird rattle coming from somewhere around the pedal/front cylinder, it only happens when engine being with light pressure on the rear brake. Any ideas what could be causing it?

 

Is your Jake Brake loose somewhere?

 

lol. nah. but the rattle seems to be coming from the Cam chain area, i tried tightening up the heat shields, but i still get the rattle whenever im slowing down, any ideas?

 

Might want to check the runout of your rear disc.