Frankenstein (1931)

The LaserDisc* is far and away the best sounding version of this.

The very first Universal DVDs are probably the worst, having been hit with heavy noise gating that wiped out everything below a certain volume -- so despite having moderately more high-end detail than the others (even the LaserDisc, which probably did undergo some high-end roll off) it's riddled with warbly-sounding artefacts everywhere and just sounds strange.

The 75th anniversary DVD and the blu-ray sound similar, with lots of noise reduction and a loud low-frequency noise floor that sounds almost like shellac.

The LaserDisc is missing the "Now I know what it feels like to be God" line. 

*Update: It's actually the Japanese CIC Video LaserDisc that was sent to me, not the US MCA LD (although that disc very likely sounds the same).

Frankenstein (1931)

Heavy, heavy noise reduction/filtering on the blu-ray mono track. See: Clip 1 and clip 2.

The VHS audio is much, much better, despite retaining the censored bits from the '30s, and the LD is reportedly similar (but without the additional noise of VHS tape, obviously).

However, perhaps even more disturbing are the reports that this mono mix of the film, the one that's been showing up on home video for decades now, is possibly just a hodgepodge of a variety of sources put together in the '70s or '80s for the film's first reconstruction. Edits are discernible and, astonishingly, many effects (ambient sound and even music queues) are often mistimed or absent altogether. The Spanish dub on the blu-ray has much, much better fidelity, and has all of these sounds intact.

An argument can be made supporting the notion that these sounds were intentionally removed from the English mono mix before the film's initial release, however there is compelling evidence within the track itself to suggest otherwise. More on this later, as additional... research... is done by a devoted fan.*

*NB: not me.