Aliens likely exist but.....
Do you think they're intelligent enough to have been on Earth or to even know the human race exists?
1. I want to make it clear I think all the area 51 stuff and flying saucers is bunk. I don't think we have any proof any alien has ever contacted us or "crashed" here.
That said, if one accepts the vastness of the Universe (literally more stars than grains of sand on every beach, and each of these with multiple planets) the position aliens don't exist, as "alien" as the idea seems, is silly and shortsited. Accepting this fact and being that our only example to go by is humans, and it seems regardless of likelihood that some being forming intelligence, then increasing intelligence exponentially is possible.
It is very realistic that some other species, or several, have done this on other planets.
Given our rate of advancement, and that our sun is third generation, it is not at all unlikely that some planet orbiting a 1st or 2nd generation sun would be billions of years older than us, and given what we know of an intelligent being's capacity to increase its knowledge base and at what speed. It is very likely something out there knows about us.
Whether they care, and whether we are just one of millions of other living planets they are aware of is a completely different matter.