99 XK8 I have an engine noise that sounds like a radiator cap releasing pressure but its coming from the center of the engine and it varies with the RPM and is like a vacuum leak but there are no engine codes anyone experience this?

 

I had just replaced the vacuum lines with regular vacuum hose and it was collapsing due to the strong vacuum and now it must be replaced with a more rigid vacuum hose. Thats why jaguar used plastic hose but that becomes brittle due to heat and leaks.