Obvious signs would be swarf aroud the hub area if any backing out of cushes etc was occuring etc.
I would imagine its not too diffuclt to at least narrow it down, with a mate to push the bike along and you listening.
Could it be a bearing on the way out? Sticking when the weight of the bike is on one side but not the other??
I think you have answered your own question really...if you can't find out for sure visually, then it may need a strip down. Not a huge job, and will put your mind at rest.
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