Is your A/C switched on at the time of engine start-up? There's 2 scenarios here; 1: I've seen plenty of cases where the belt isn't tensioned properly and it makes a rather short loud squeal sound on start-up (sometimes drawn out). Toyota cost-cutting is the problem here as the belt tension is done via the old manual method instead of an automatic tensioner (why Toyota?!?!?). 2: The A/C system is either undergassed or overgassed, which I suspect is your issue. This will definitely cause some strange noises such as the ones you describe. A/C for Ascent/Conquest/Levin SX is dealer fitted, and PD fitters are generally not mechanics, so they never do the job properly. I'd ask for the pressures to be checked, and check your belt tension as well. Definitely not the A/C. I always switch off everything. The mechanics i talk to on the phone thinks the driving belt wasnt adjusted properly. I'll probably take it in sometimes this week. Such a waste of time.