Long time reader, first time caller

My company did a DX plant upgrade (A/C) and have installed a 134a bitzer screw (around 300kw capacity) which was sized and designed by a separate engineer. The discharge pipework has a very loud internal resonance coming from 2 spots (*): brief pipe rundown

Rises from compressor then horizontal 2m
*a straight that drops and climbs with two 45 degree bends with 1m in between elbows
5m then right bend then 15m
*a left hand bend, runs 1m drops vertical 0.5m then straightens horizontal (loudest)
Then outside to condenser

The unit is still slightly undercharged going off vessel on pump down (DX so unsure of full), the discharge pipe work is 2" 1/8, no mufflers/eliminators

Addition of gas towards 'full' has helped and reduced pulsations a little
All fixings are tight but not really relevant given the nature of the noise
Pressures run around 780-800kpa (pressure controlled) and 210 kpa

Neither myself or my supervisor have had much experience with this issue, can anyone provide insight into what's causing the noise? And/or a solution?