On pretty much any manual gearbox changing down to a lower gear is harder on the synchros than changing up. this is because when changing down the synchro has to grab hold of the relevant gear and spin it up to a speed matching the lower gear you are trying to engage. Changing up to a higher gear is not so arduous because the gear you are selecting will be revolving faster than the one you are trying to match it to so it's going to be slowing of it's own accord anyway. So, if you have a worn synchro cone it's much more likely to crunch on a downward change than an upward change. Of course as wear gets worse it'll crunch in either direction! So the fact it's crunching on a downward change is probably due to moderate wear on the 2nd gear synchro ring - Often 2nd is the first to show wear, especially if the car is driven at slower speeds - around town for instance. As a matter of interest, a car driven mainly at higher speeds, out in the country perhaps, will often wear the 3rd gear synchro first.
It's just possible the problem may be being made worse if the clutch is dragging. You can check this by, with the engine running and the gearbox in neutral, depressing the clutch pedal and waiting for a few seconds with the pedal fully depressed. Maybe 5 seconds or slightly longer if you want to be sure. This will let the driven plate and input side of the box spin down and come to rest. Then try to engage reverse. Reverse gear - on most gearboxes - has no synchro so if the clutch is dragging the input side will still be spinning and you'll get a "nice" crunch. If the clutch is "free" you won't get a crunch.
I don't tend to have the radio or other entertainment on when driving as I prefer to listen to my car and observe and listen to the vehicles around me. I often hear a crunch from a car selecting reverse to exit a parking space in the supermarket car park. Often not because it's clutch is dragging but because it's driver has selected reverse almost before depressing the clutch pedal. This won't happen when selecting first gear because it has synchro to force the driven plate and input side of the box to stop rotating and thus match it's speed to the output side of the box, which is not rotating due to the vehicle being stood still. Reverse has no synchro though so you have to give the input side time to spin down to a stop. Crunching reverse is not good of course because you are milling minute slivers of gear metal off into the oil which can then merrily travel round all the other components of the gearbox - ball and roller bearings, bushings, etc - and shorten their service life. It's all very easily avoided if you just let the gears spin down. I accomplish this by counting bananas! So it goes like this: Push the clutch pedal down to the floor and as it hits the floor say to yourself "one banana, two banana" and as you finish then move the gear lever into the reverse position. "One banana, two banana" said not too quickly, should take around 2 seconds or slightly more which should be enough time for the input side to spin down and, pretty much, come to a stop if the clutch is freeing as it should and there's no binding of the spigot - most of our smaller Fiats don't have a spigot though.
In my opinion one of the first things you should always do when you buy a vehicle, regardless of the age of vehicle - unless it's new - is to change the gearbox oil. Precisely because you can have no indication whether the previous driver has been a "gear crasher". Synchros lead a hard life so will benefit from new oil too, as will all the other gearbox internals. Get the gear oil nice and hot, you probably need to drive 10 miles or so to do this, which will get it nice and hot and thin and tend to mix up "foreigners" so they are held in suspension in the oil. Now it will flow out nicely, taking a lot of the "rubbish" with it. Be very fussy about the oil you refill with, especially if it's a more modern vehicle. Lubricants are almost vehicle specific now a days so I will only use the actual oil specified by the manufacturer and I wouldn't add "improvers" of any sort. It may cost slightly more to buy the actual manufacturer's specified oil but transmissions don't take much oil and you're not changing it often (I recon around 50,000 miles on family vehicles) so the extra cost is minimal in the grand scheme of things.
PS So, after all that, I think you are right to conclude you've got a synchro problem!
