Factor $(x+y)^4+x^4+y^4$

Note that $$(x+y)^4 + x^4 + y^4 = y^4 ((x/y+1)^4 + (x/y)^4 + 1)$$ and see if you can factor $((t+1)^4 + t^4 + 1$. There is a quadratic factor.