its the turbo flutter you hear 1st then the dump valve, my last few classics were the same and the blobeye was when i had the wing mount air filter fitted
is the car a PPP ? if so it will need a remap i know of a few that did this after changing the same parts you have, once the car was mapped it was all good
mine does it as well and i know its due to the ppp map, but i see no point in mapping it till i get all my go faster bits
i just drive round it
if you get a new one, i would recommend forge, i have had a lot of makes over the years and always gone back to forge, last spend was £250 on a turbosmart within a month it was sold and another forge one bought