Q: My car hums when I try to start it on cold mornings. Battery starter and alternator tested and all are fine. I need help please!

A car battery can appear to be 100% "charged" and still be essentially useless. The only way to determine the viability of a "used" battery is to perform a load test on the battery at a professional battery shop or with a mechanic who has a load tester. If the battery passes the load test (even if it marginally "passes" the test, absolutely get a new battery), the starter relay and/or solenoid are checked for power (i.e., is full battery voltage getting to them and is there close to zero voltage drop). If they are getting power, the starter is probably no good because the bendix drive will typically fail after high miles. A completely useless starter, that is one with a failed bendix drive, will test 100% perfect on a starter tester at any of the big box auto stores, simply because those are freewheeling tests with absolutely zero load on the starter. Once you load the starter, as in try to actually start an engine which presents significant mechanical resistance, the starter simply does not work. My advice is schedule a quick no start diagnostic and YourMechanic will absolutely get you up and running without further problem.