I had an 84 1.6cvh for the last 13 years, 72k on the clock when I sold it, never sounded like you describe and if anything it pretty much purred.
The only time it did have an odd noise, which kind of sounded like you describe, it was erratic for a few years then got worse, ended up being down the the bearings in the alternator which once refurbished was back to normal.
