Sounds like an exhaust leak, but it goes away so fast, it makes me wonder if it is something else...It is possible the leak is so small it could go away with minimal engine heating that fast?


2001 m5 3.8 is what I am working on

 

Sounds like its just lifter noise since it goes away after a few seconds.

Its common.

 

so seafoam it?? What is the solution?