I had that issue with a Sony 761E - replaced the laser then found out the problem was actually just a little ribbon connector.
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My 303 occasionally 'spits' ie a very short, intermittent buzz which lasts less than half a second. The music behind the noise remains completely undisturbed though so it's probably not laser/disc mistracking. Discs are read very quickly after insertion, less than a couple of seconds.
Leave the player running for half an hour or so and all this goes quiet, as though it's been warming up.