Couple places for investigation:
-drivers side boost pipe to intercooler, these have a rubbish clip and seal design and alot of us have found oil sludge weeping out of them which points to it not being properly sealed. The o ring seals may have gone, cheap and easy to replace.
- if you've taken the old intercooler out and back in, possible could have damaged it? I've heard of a couple of owners finding tiny cracks in the intercoolers before.
- PCV and pcv hoses can go, though not sure you'd have a loud whooshing noise.
- DV but unlikely as you say its been done recently
- rocker cover gasket leak
I was chasing a similar issue on mine, it was only at peak torque in higher gears and only about 1/3 times would it happen. After fitting an intake you can hear the boost leaks very well! I changed tons of stuff and was convinced it was the intercooler/connection somewhere but R tech tuned it recently and said it was the rocker cover gasket. After tuning it was far worse and very loud, due to the extra boost. On my list of things to change in next few weeks.