still another possibility is that the tonearm's cue DOWN is sudden, causing a rebound of the stylus. ( I mean, this is a brainstorm proposal of possibilities).
Still again, the tonearm itself (near its pivot, or behind its counterweight?) is hitting / rubbing something unsuspected. OR tilted mounting of turntable, OR bouncing surface for the turntable, OR faulty antiskate?
And also, the records themselves MAY be at fault with some sort of debris, scratch, or vinyl bubble (looks like a bubble coming up from the inner surface of the vinyl) near the rim? These are extremely rare possibilities, ALL of which I have confronted over the years.
Regards and best wishes,