\[ \boxed { {x}^{2}{\frac {{\rm d}^{2}}{{\rm d}{x}^{2}}}y \left ( x \right ) -2\,x{\frac {\rm d}{{\rm d}x}}y \left ( x \right ) -4\,y \left ( x \right ) -x\sin \left ( x \right ) - \left ( a{x}^{2}+12\,a+4 \right ) \cos \left ( x \right ) =0} \]
Mathematica: cpu = 0.157020 (sec), leaf count = 38 \[ \left \{\left \{y(x)\to \frac {-2 a \sin (x)-a x \cos (x)-\sin (x)}{x}+c_2 x^4+\frac {c_1}{x}\right \}\right \} \]
Maple: cpu = 0.032 (sec), leaf count = 33 \[ \left \{ y \left ( x \right ) ={\frac {{\it \_C1}}{x}}+{x}^{4}{\it \_C2} -{\frac {ax\cos \left ( x \right ) +2\,\sin \left ( x \right ) a+\sin \left ( x \right ) }{x}} \right \} \]