F150mkr

Im not a repairman, but here's two WAGs- First, does it only occur when one (or both) turbos are engaged? If so, possibly a vacuum deficiency from a faulty connection or possibly even some sort of issue with the AUX vacuum pump. Second, an obstuction within the system such as a faulty A/C pressure switch, solenoid, dryer, or even foreign matter within the lines. Best wishes, and THANK YOU for buying our truck!!! P.S. Tomorrow I'll ask some guys at work fi they have dealt with this before, and I will pass this along to the PVT (a team of engineers that solve issues like this-)