Is it different in all flight regimes?
In many other helicopters with intakes that are exposed to the airstream, there might be the possibility that the airflow entering one intake is not as good as the airflow entering the other intake. The difference would obviously be at a minimum in a hover and maximum in cruise.
With the EC-135, the intakes are buried in the transmission area. Unless you have something not being right in that area, you might look at the thermocouples as previously mentioned.