EC135
Flight Crew Rotorcraft
Situational Awareness
Aircraft Equipment Problem Critical
Flight Crew Overcame Equipment Problem
Environment - Non Weather Related
After landing at ZZZ and bringing the engines to idle I noticed a whishing sound coming from the main rotor system.  There weren't any associated vibrations.  The medical crew did their walk around and after getting in; the flight nurse also stated that she heard the same noise.  I brought the engines to flight and the noise was still present but not as noticeable.  Looking at the disc path plane revealed nothing.  I raised the collective enough to get the nose to raise and almost immediately plastic sheeting was seen leaving the main rotor system.  I shut the helicopter down.  Upon walk around plastic sheeting was observed on two of the main rotors; three of the fenestron blades; on the stator vanes of the fenestron and on the protective covering over the oil cooler intake.  The helicopter was placed out of service and maintenance was notified.  The mechanic inspected the aircraft and an operational check flight was completed.  No damage was found.  I never saw where the plastic entered the rotor system.  There was a construction dumpster underneath the helipad that was only partially covered.  There appeared to be a similar type of plastic in it.  Make sure that the helipad and surrounding area is free of FOD and that any sources of FOD are secured.
EC135 pilot reported that FOD became caught in rotor blades during landing.