[ejsharp]

Yes it does not sound quite right. There are other things... like a loose nut on the end of a cable, poor body ground for the negative cable.

Where does the nut for the starter end of the positive cable connect to the solenoid? Is it outside the manifold and behind the engine near the firewall? If so it may be readily accessible to be loosened or re-tightened yet out of sight from an unsuspecting observer.