I have a Shimano 7-speed freehub on one of my bikes from the late 1990's that has a fairly high rolling resistance through about 1/4 of its revolution and the rachet also changes pitch.
I'm assuming it's kaput as I don't think there's any way you can service it.
I looked on ebay and there are multiple different Shimano 7-speed freehubs such as:
I haven't a clue which one would fit, if either. Suggestions?