The pops and screeches definitely indicate a problem with reading data from the hard disk.

Please give specific numbers when you say the "temps seem normal".

Unless your installation location is situated right next to a heater duct, in direct sun, or double-Din'd in with a hot CD player, temperature is unlikely to be the cause of the problem, it's just the catalyst that makes the problem crop up.

If it's possible to reproduce the problem indoors, put a recent hijack onto the player, play the unit until the error happens, then reboot the unit right away while capturing a boot log. Then post the boot log here. Info about the hard disk problems will be in the boot log, where Hijack is reporting the IDE data tests.