My 69 F250 /390 recently developed a tapping noise under load. The noise is similar to a fan hitting something. It won't do it in park, only when pulling a hill or similar load then fades away as the load lessens. It seems to have begun after installing a new starter and the noise may even come from that area but it doesn't make sense. If the starter were hitting the flywheel it would do it in park also I would think. The starter in in properly and mounted solidly. I'd appreciate any suggestions. It has me puzzled.