As I have been tweaking my Emacs configuration, I noticed that I was getting warnings like the following in *Messages* during Emacs startup:

ad-handle-definition: `tramp-read-passwd' got redefined

I looked into it and these warnings are generated when functions are redefined with defadvice. Most of the warnings I received were coming from third-party packages I had installed, not my own configuration. In any case, they were not helpful, just noise during Emacs startup.

Like everything in Emacs, this is configurable. Turning off the warnings is as easy as adding:

(setq ad-redefinition-action 'accept)

To your .emacs file. I found I had to add it fairly early to ensure that all the warnings were removed.