New (Faulty) SL3 Problem

Hi folks - just joined and looking for some advice on my new purchase. My 'new' SL3s were delivered yesterday and first impressions were great; however while experimenting to find the optimum position for them I noticed a low level pop-pop, popping sound from the left channel.
Swapped them around this morning and the problem is now on the right, so it's definitely the SL3 and not the amp (Meridian G57). Also, on connecting mains power the 'good' speaker is silent, the other buzzes gently for 15 seconds or so before settling down. The popping noise is at a low, constant level, unaffected by increasing/decreasing music volume, and gradually dies away when the source is disconnected. (Incidentally, the amp needs less drive from the pre-, but is running hotter than previously).
I'm guessing one or more capacitors needs replacing, either in the psu or the crossover (they are around 14 years old, after all). Presumably won't be able to reach ML until Monday, but would really like to know if this is a common issue (haven't found it mentioned on here, yet) and how serious it is likely to be. Legally I have a couple of weeks or more to return them to the seller, but apart from the hassle, I'd much rather negotiate a discount and fix them if possible. It looks as though (in the UK) it's likely to be a DIY job, so any pointers would be much appreciated. Thanks.

For starters leave the speakers disconnected from the mains for 24 hours, vacuum them, then reconnect and listen to them.

I would suspect either dirt causing extreme leakage to the stators, or a poor connection to the diaphragm, either at the solder joint to the diaphragm or from the copper strip to the diaphragm. I suggest putting on your magnifying glasses and using a soft brush while vacuuming around the ESL panel, paying special attention to the sides and top of spacers. Then ensure the ESL sandwich is clamped together properly by the rails.
What happens to any noise as you squeeze the ESL sandwich together by hand all around the panel?
You can rule out a PSU problem by swapping panels.