Boxster wont start after shut off on short trips

My 2000 Porsche Boxster S will start and run but after turning it off occasionally It just turns over and doesn't fire/start or even sputter. Hours later it will fire and start like there is nothing wrong. I do hear a howling sound while driving occasionally. Replaced fuel pump relay, same deal. Would bad fuel pump or pressure regulator explain symptom?

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[Casey at Pelican Parts]

Very common...99% sure you have a faulty charcoal canister purge valve (aka fuel regeneration valve?!). The purge valve is located in the engine compartment on the left side beneath the intake. Part number: 996-110-129-06-M100

- Casey

[JFP in PA]

I would also look at the crank position sensor, which are well known to act up when warm, and then be fine when they cool off. When the CPS fails, the car often will not code, but won't start when warm because the DME does not see the engine turning and shuts off the fuel and ignition.