You have a way to log boost data?
Measure blocks are 115 and 118 with Vag-Com. Do your best at getting some data to see what the target and actual boost is.
Mine makes a sound perhaps similar to yours but only if I do full throttle from a low rpm in those gears for data logging. All other times I downshift.
I believe it is just not enough air for the compressor to push when ECU tries making target boost. Called compressor surge. Best way to explain this is the compressor chops through the air rather than pushing the air. So, it's an imbalance on both the exhaust and inlet sides. In other words, the exhaust is spinning the compressor so fast that the compressor needs a balanced resistance to prevent surge.
If happening at just when at low rpm's...try again at higher rpm and post what you find. Might just need to keep it in the power band when planning on full throttle mode and downshift
What's the diameter of the intake tube? You have the intake but no tune?