Strange noise then shifting UP

[Sprunkas]

Hey guys, for few past month I had this strange noise then car is shifting UP. It didin't sound like metal or ruber. Its strange muffled sound. Firstly I thought that is Gearbox or engine mount. 

Then I'm driving in city and car shifts through 2-3-4-5 gears I can hear this noise 1-2 times (it's sounds like "blump" or "blump blump" 😄 ). But today I was driving with Lap Timer menu and saw that then this sound appears Boost scale starts to jump up and down. It happened then I accelerated from 60km/h to 80km/h with cruise control, and then car reached 78-79km/h Boost scale started to go crazy up and down (Car wasn't jumping or anything, I just heard this noise). I pressed gas pedal and everything came back to normal.

This sound appears sometimes. Last time it was few days ago. Mostly then engine is fully warm. Sometimes I can drive for few hours and this noise wont appear. 

I have this car for four months, I bought it with seized engine, we fully rebuilded engine and for first month everything was fine. I know that previous owner tuned this car in JDEngineering, it has sticker and BIG Wagner intercooler. And this noise appeared after +/- month of driving.

Main turbo is okey, because I checked a few weeks ago then I changed air filter.

Maybe someone had same problem or has any idea where I should start?