G, Could it be that your alternator belt is whinning ? They do this after some time. You mentioned you had been failing to start the 6 for a few weeks, the rubber may had hardened, Don't be tempted to tighten the belt, get a new one, IF you left teh engine running I think you'll find that the squeel will go once the fricton has heated teh belt, softened the rubber & the belt then grips the pulley's.
Start her up leave it idle for a few minute's, then just give it some gas for a fast idle, then increase the rev's I bet the noise will have gone.
Hoping this works for you,
2x 145, 4x 75, 4x Sprints,a 156, 146 now a 155