\[ \boxed { 4\,{x}^{2}{\frac {{\rm d}^{2}}{{\rm d}{x}^{2}}}y \left ( x \right ) + \left ( 4\,{a}^{2}{x}^{2}+1 \right ) y \left ( x \right ) =0} \]
Mathematica: cpu = 0.012002 (sec), leaf count = 32 \[ \left \{\left \{y(x)\to c_1 \sqrt {x} J_0(a x)+c_2 \sqrt {x} Y_0(a x)\right \}\right \} \]
Maple: cpu = 0.031 (sec), leaf count = 25 \[ \left \{ y \left ( x \right ) ={\it \_C1}\,\sqrt {x}{{\sl J}_{0}\left (ax \right )}+{\it \_C2}\,\sqrt {x}{{\sl Y}_{0}\left (ax\right )} \right \} \]