spring 9rattle snake) noise when cold

[blanc]

Hi All,
 
This is an unusual one. My car makes a sound like a spring or rattle snake when cold. When driving slow ie 2-3000 rpm. Is this normal?
 
Car was rebuilt and cas compression over 7 on both.
 
Any Ideas?

[neil_jdmr]

Sounds like a heat shield fella, try checking the cat and the one on the downpipe.