Help with ringing bass from Dynaudio C1


I recently replaced a pair of Silverline SR17.5's with some Dynaudio C1's. I love the Dyn's, but one thing is driving me crazy: on some passages with a deep bass drum (e.g.,Young People's Guide to the Orchestra on Mr. Britten's Orchestra), the bass starts ringing, obliterating other frequencies and sounding very much out of control. I have tried putting an acoustic panel in back of the speaker. That helps some, but the bass is still resonating too much. It sounds like one note in particular, but I can't say for sure.

System:
PWD mkII via ethernet bridge
Bel Canto Ref 1000M
Audioquest Sky XLR, & Volcano speaker cables
Audience AR6T conditioner
alsteinnj
You need a hih-current amp that exhibits better control of the woofers' excursion...

-RW-
Try moving the speakers back or forward 6 inches at a time
and then inward till it is least offensive
Best JohnnyR
Do you think there is a defect in either the speakers or amplifiers? The setup sounds absolutely perfect except for being out of control at the very bottom. Any bass above that sounds quite tight. However, the bottom is so out of control -- ringing for several seconds --, it is hard to believe that such highly reviewed products could have such a glaring flaw without someone else mentioning it.
what are the speakers standing on? if they have feet or footers, tighten them (or remove them if the footers are on a platform); are the screws lose which hold the driver?
They are on Core speaker stands. I tried picking up the speakers and holding them while they were ringing; it made no difference.

The driver screws are tight.