This whistling/chirping issue is happening to me since installing a JB4. I cannot reproduce the sound on map 0, but on map 1 and map 4 I can reproduce it (and the JB4 should be doing stock map on stock 4...). I don't know why I don't get the sound without the JB4, and I hope the JB4 isn't what caused the valve to break. I've owned the car for 3 years and I've not done any kind of pressure test. I'd hate to replace the valve cover only for the new one to break as well...
I couldn't identify the problem with smoke, but Vespa kindly helped me out and it appears my PCV valve is blown as well. I think I've verified it with a small tube from the valve and putting it near a small amount of water it sucks it in constantly.
https://www.dropbox.com/s/ccqukqgf02...41.25.mov?dl=0
Hope it can help someone