It is often said about this movement that it is written in 3/4 meter, as a minuet should be, but sounds in 2/4. I doubt that is what you hear. It isn't a simple hemiola, either. One of the trademarks of gypsy style is rhythmic freedom in the violin, who often plays before or after the beat. I think Haydn is creating his own version of this effect. If you look at the score, the violins are offset from the viola and cello. Considered by themselves, the viola and cello are doing this: a simple bar of 3/4 followed by a bar in which the second beat is accented, followed by a hemiola where two bars of 3/4 become one bar of 3/2. Followed by thee bars of 3/4. The violins are doing something similar, but a bar earlier! Upbeat, 3/4 with second beat accented, bar of 3/2, two bars of 3/4 with second beat accented, three bars of 2/4 (which sounds quite different from one bar of 3/2). That's what it sounds like to me! Your mileage may vary. What I hear is this: the violins are a measure ahead of the viola and cello and both groups are using accents and hemiola to confuse the listener as to where the downbeat is. The effect is not 2/4, but polyrhythm! In other words, there are two layers of meter and they are not synchronized. For contrast, the trio is in utterly humdrum 3/4 meter with a cello solo. The contrast between minuet and trio is metric! Cool.
Just in case you think I made all this up, here is my metric analysis of the first half of the minuet:
|Click to enlarge|
Of course, my music software won't allow anything as odd as this, so I had to cut and paste and still the automatic spacing confuses things a bit. But this is how I hear each part. They are moving through 3/4, 3/2, back to 3/4 and then 2/4, but the violins are ahead of the viola and cello. Wacky guy, Haydn...