Thanks Stuart - I'd found the Meridian tech note on identifying the tweeters, and they're definitely using the H539 ... plus your thread on changing the ferrofluid is exceptionally useful, so I might give that a shot. Do you happen to know if there's a modern equivalent of the H539 from SEAS if the ferrofluid change doesn't sort out the issue?

Cheers

Office: MacMini + Roon -> MS600 -> AR LS-9 -> M60s (1993 vintage)
Home: [AppleTV -> HD621] + [Roon -> 218] -> G65 -> DSP5200HC + DSP5200s + DSP3200s
Being a JAFA in Auckland, New Zealand