I have a 2wd saff, stage one, 4x4 intercooler and hybrid T3 turbo. the car holds 14-15psi. I am using a forge dump valve (6 allen key type with diaphram) The turbo is only 6 months old.

Today when driving and comiong off the accelerator, instead of the usual dump valve whooshm i am getting the chatter noise like you do when there is no dump valve fitted.

I haver taken the dump valve off, stripped it, cleaned it and put it back on but no change.

the dump valve is fitted on the turbo side of intercooler, and this has never happened before, until today!!

Any Ideas?

The car still seems to be boosting to usual 14-15psi
and goes down to -9psi vaccum. (these figs on my nomad boost guage)

CheeRS