I know the previous owner and he has told me that there was absolutely no hidden defects or issues with this rig whatsoever. In fact he showed me the maintenance records done to it by a local motorcycles dealer. He has even suggested that we take it to the dealer and have it checked there. I declined because I trust the guy.
Now as far as that weird noise, it could be something normal as the pistons underneath this thing are massive. At low speeds the noise could simply be the normal engine doing its normal business.
What HD tail light are we talking about?
The only HD item on this rig is an oil pressure gauge the previous owner put in there. I personally do not know what its use is, but it looks cool.