Hitachi 3D40e Woofer Noise

[retroclub]

Have been noticing that the right woofer on my Hitachi 3D40e is making a bit of noise kind of like a vibration when the bass is cranked up.
Just wondering if anyone knows what could be causing the noise and if I can remove the speaker grills easily to get into it.

It's one of these -

 

[hopey]

It could be the balance or volume pots or the coil in the speaker. The grills are not removeable you can access the speaker from behind, then you can press your finger on the speaker to see if you can reduce the noise as it's playing.