Could it be Pinking?

[Martin Baker]

Thanks everyone for prompt suggestions.

The noise is definitely more like a loose panel resonating but I can't find anything. I have checked that the floor screws are tight, I have in the past tried isolating the flywheel cover. One new idea is to make sure the exhaust pipe has enough clearance from the chassis.
Other points:

• Always try to use high octane low ethanol fuel.
  
• no run on.
  
• plugs show running rather rich and poor consumption
  

In answer to the various points raised:

• crank & flywheel where balanced
  
• front cam bearing has standard dual O ring and cap screw mod
  
• tried emptying battery box/wrapping tools in rags
  
• compression ratio - I undertsand the Ricardo head is 6.5:1
  
• car not new. Have experienced previously but came to fore during 700 miles on TOTIE last week, especially the 140 miles each way.
  
• once in resonance range, noise increases with engine revs.
  

I'll keep exploring but grateful for any more ideas.