I hate HOAs and would find out of the owners of those other cars are also being scrutinized (or if they're HOA members and being 'overlooked,' as a result). If the owners are indeed members, I'd stuff it right back in their faces and tell 'em to pound sand. Then threaten to sue the HOA for discrimination, harassment, and whatever other small civil court things that could be defensible.
I'd first go over the by-laws with a fine-tooth comb, run it by a lawyer if needed, and stuff it back in their faces when no such rule exists. How much legal power does an HOA have, anyway? Did you sign anything when you moved in?
If it's in your driveway, they shouldn't be able to do anything about it... but parked on the street, they might try and have it towed, which might just be within their jurisdiction to do so. Definitely need to find out what their rules are and exactly how much power they actually have.
Chances are this is probably more about the drip marks on the street. It also sounds like there are a handful of Karens with bugs up their tailpipes for one reason or another.
