intermittent thudding bass noise ?

[saabste93]

Hi all i have just come across a strange thudding sound from one of my speakers intermittent if you will, its only just started after i swung into my driveway and even when all the voll is down its the same sound (loud bass noise ever 3 secs)
puzzled saab owner here , all advice welcomed..
Saabste93

[Roto]

Does it seem to follow any engine pattern? May be the DIC cleaning cycle? (when you pop the hood you hear the engine head buzzing right after you shut the engine down.)