I have a noise that sounds like a distant vacuum with a high pitch sound that may be a high pitched whistle sound coming from the intake manifold assembly somewhere around the “big ball”. When the engine speed increases the high pitch disappears. Is this normal? It also seems that the engine is a bit weaker but that may be due to the snow tires. How do I check for a vacuum leak to diagnose this?

Thanks 92-960, 195 000 km