my car has a chip, full mongoose system, and pipercross induction kit. however, when the chip was fitted, the boost was set to ideal for the exhaust. im MOT'ing it tomorrow so have fitted the standard exhaust system back on.
problem is, when accelerating hard from low revs, once it reaches 4000rpm, there is a very high pitch scream (is a fluctuating scream and sounds like the turbo). you can rev it gently to the redline and no noise, its just on boost.
what is this, is it due to the exhaust restriction?

any help appreciated.

thanks

ian