Sheetmetal scraping sound from rear of Kirkham

[TimG427]

I’ve got an interesting noise issue on my bronze Kirkham. After about one mile of driving I hear a strange sound like something bouncing or rubbing against sheet metal. This immediately turns into a screeching noise and goes away after about two seconds. It will reoccur about every five minutes. At first, I thought is was something loose in the clutch or flywheel getting bounced around in the scatter shield like a stone or piece of metal. There is an open area in the scatter shield and nothing is in there and all the bolts are in place for the clutch. The clutch works perfectly with no shifting issues, so I’ve ruled that out. I raised the rear end and removed the wheels. There is no evidence of tires or wheels rubbing on anything at all and there is plenty of clearance everywhere. It doesn’t appear this is in the differential as I’ve had bad differentials before and it’s not a tinny type noise like this is. Also, I don’t feel any vibration or grinding of gears, the car runs fine. If I shift to neutral while the noise occurs, the sound continues for the same two second or so period. Its always the same noise with no variation due to speed or RPM.

I thought it may be the fuel pump as this is mounted adjacent to the differential on a Kirkham. When the sound starts, I’ve turned off the fuel pump and the sound will continue as usual. Maybe the fuel tank shifting? It seems to be mounted soundly in place. The sound seems to be coming from the rear of the car and I haven’t been able to reproduce it while the car is stationary, but I’ll try to let the car idol for a while to see if that creates the sound. My last thought is that the headers/sidepipes may be expanding internally and making the metal to metal noise, they are some big honker pipes and mufflers made out of stainless steel. It really sounds like something rubbing against sheetmetal. Any thoughts from fellow Kirkham/Cobra owners would be appreciated. I’m driving the Cobra regularly as right now it doesn’t seem to interfere with performance. With another week of wet weather predicted here in Austin, I may not be able to get the car out for a spin.