Has nothing to do with the gear teeth being rounded or square tipped.
The difference is whether the gears are helical or spur (straight cut) gears are used. The contact surfaces in helical gears engage and disengage gradually as opposed to spur gears where the teeth engage across the entire surface at once which causes greater stress and increased noise (which is perceived as "whine" at higher speeds).
I cannot think of a single normal modern car that would use spur gears for the forward gears, even for first. While there are high-performance straight-cut setups available and while some exotics may use spur gear setups, even the venerable Muncie M-22 "Rock Crusher", for all its legendary noisiness, used helical gears.
In general, spur gears are reserved for non-constant-mesh gears (for example, reverse in most manuals is not a constant-mesh gear) because spur gears can slide in and out of contact along their axes fairly easily whereas helical gears can't easily be slid into and out of contact. Also, spur gears are much, much, much noisier than even a noisy helical gearset.
Noisy helical gears (Muncie M-22)
True spur gear setup (racing sequential gearbox)
For any common modern street car made since the M-22 went out of use in 1974 though, gear whine in any forward gears is unlikely. Generally what people hear is belt whine.
ZV
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