Rattling with dust cover of ESL

[Fabien Lefebvre]

Hello,
I have juste re-built an ESL 57. I have a minor issue with dust covers:
although correctly tensioned (using the same weights applied to the
diaphragm itself), I observed some rattling noise when excited at very
low frequencies : around 40/50Hz.
This has no impact when playing music but with test tones this is annoying.
I say "correctly tensioned" because there are not any wrinkles. Yet if I tap
using a finger, it vibrates longer in time than some other panels I have and
that I assume were never re-built.
My question: are they too much tensioned or not enough ?
If I paint the dust covers as Quad used to do it, will the added weight lower
the resonant frequencies and thus remove this trouble ?
I did not observe this problem with my other panels (original) but with these
ones - which are certainly suffering from aging - there is almost no output at
those frequencies.
Thank you.

[Fabien Lefebvre]

Results from last trials: it seems that it is more a question of overload:
* if I reduce input power, this rattling disappears
* original panels have about the same behaviour

It might be that Quad II + ESL57 cannot handle very low frequencies at high power