[convincor]

Hey Bob,
Mine has very similar sound. Won't do it if you rev with no load on it.
Hard acceleration it won't do it. Only seems to be around 2000-2500 rpm under very lite load... Havn't found it yet. Did it with standard adjustible rockers and still the same with Erson rollers.
One thing I did notice is the intake gasket is starting to look like it's going.
Could be split on the bottom of a port and drawing air through a small split??
See toward the end of this thread- Spark plugs: 7 tan, 1 black