Problem with Markbass TA501/152 Cab

[darth by tor]

Hey All,

Apologies if this has been covered in another thread.
I run a TA501 Markbass Head through a Markbass classic 152 2x15 Cab.

The head is three years old, the cab just over year.
Recently Ive noticed a shimmering almost chorus type effect when playing The D or G string.
Ive tried different basses and adjusted the settings etc, but not being that technically minded I'm stumped, anyone have any ideas or has come across the same issue?
Thanks in advance

[craig.p]

Tough to say, but the first thing I'd do would be to make sure the drivers are still socked down tight, and then the speaker grill, too, after you put it back on.