Hissing when idling from breather hose intake

I've read elsewhere that the PCV on some Jags do make a hissing noise due to it's corrugated design. If you have a vacuum leak in the PCV or the intake, you would see lean condition codes. Just make sure the crankcase vent valve , hoses, and o rings are in good shape. If your mechanic doesn't specialize in Jaguars he or she may be misinterpreting the hissing as an actual fault when that is not the case. PS I would NOT seal up the PCV or breather vent hole, that's a recipe for disaster.