Hissing from Oil Dipstick

I have heard some hissing upon shutdown on my 2000 mile 318 with stock internals and a
Comp XE268 cam and lifters. I have cast pistons, moly rings. It runs great, but have heard a two or three second long hiss coming from the dipstick. I opened the hood today, shut the motor down and quickly pulled the stick. Released pressure and the hissing stoped.

Does this sound like a restrictive ventilation system? The pcv is not too old, but I put a different closed tyoe breather on it that I had a hard time blowing air through. Could this be the culprit? i cannot figure out what else it would be.

It does not smoke at all and runs awesome. I have a K&N (very unrestricted) breather that i can use instead if needed.