\[ \boxed { {\it d4y} \left ( x \right ) +\lambda \,y \left ( x \right ) =0} \]
Mathematica: cpu = 0.004000 (sec), leaf count = 76 \[ \left \{\left \{y(x)\to c_1 e^{(-1)^{3/4} \sqrt [4]{\lambda } x}+c_2 e^{-\sqrt [4]{-1} \sqrt [4]{\lambda } x}+c_3 e^{-(-1)^{3/4} \sqrt [4]{\lambda } x}+c_4 e^{\sqrt [4]{-1} \sqrt [4]{\lambda } x}\right \}\right \} \]
Maple: cpu = 0.109 (sec), leaf count = 50 \[ \left \{ y \left ( x \right ) ={\it \_C1}\,{{\rm e}^{-i\sqrt [4]{- \lambda }x}}+{\it \_C2}\,{{\rm e}^{-\sqrt [4]{-\lambda }x}}+{\it \_C3}\, {{\rm e}^{i\sqrt [4]{-\lambda }x}}+{\it \_C4}\,{{\rm e}^{\sqrt [4]{- \lambda }x}} \right \} \]