mine also chatters but only in low revs, say before 3.5k. then after that the boost makes the dump valve chirp, i have tested all my hoses and they are fine it is literally just the turbo not having enough boost to open the valve fully in low revs, and this is with a forge split r aswell recommended for the engine. My mates have mr2 turbos and a gts skyline and theirs do it too