"When the truck is warm - not hot and not dead cold, but only say about 2-4 hours after being parked - it makes that noise like the battery has just enough power to start it" just a guess - sounds like a connection issue (positive or ground) due to condensation. & you had mentioned a starter vibrating loose issue, so I recommend removing all the connections at the starter, cleaning & applying di-electric grease prior to re-connecting. (cuz when it doesn't start it will occur @ the work possible scenario....like an on-ramp)