I did not see your car profile, I thought the actuator is boost.

But anyway it could be that your system is getting in resonance.
If you did not work on or changed something I'd check the free movement of the waste gate first.

An orifice also in the vac line to the (vac) actuator might indicate whether it is the resonance or just a restrictive waste gate.

Next look closer to the electrical parts to control the vac (I am not familiar with your engine year).

Tom