On Shabbos where there is a door that is making lots of noise or a swing outside that is making lots of noise as well that is bothering not only the person of the house but the neighbors as well may one put WD-40 on the door or swing in order to stop the noise?
Although there is no official problem with this, one should ensure it is done before Shabbos.
The swing is working fine, so that the lubricant won’t be “fixing” anything, and the fact that it will silence the creaking noise doesn’t appear to involve any Shabbos violation.
Yet, there might be an issue of uvdin de-chol (weekday-like activity). Applying WD-40 (or other mechanical oil etc.) is a very chol-dik concept, and although as noted, there is no actual melachah involved, the act is nonetheless related to the melachah of makeh be-patish.
Therefore, although under extenuating circumstances there might be room for leniency, one should certainly ensure this is done before Shabbos.
For insteresting comparisons to the questions, see: Yabia Omer (5, Orach Chaim 33, concerning opening a blockage on Shabbos); Minchas Shlomo (1:9, concerning using a microphone); Minchas Yitzchak (5:39, concerning sweeping a wall-to-wall carpet).
The last source prohibits using a carpet sweeper because of the tircha involved, and because it looks like fixing a keli; in our case, there is greater room for greater leniency, because of the lack of tircha. Nonetheless, as noted, one should ensure it is done before Shabbos.