I have a strange problem with one of my JBL subwoofers. Its the L8400P, part of the current Studio L Series.

Its always in "Standby" mode. When it gets a signal from the receiver (HK AVR630) and switches on, it makes a loud noise, a "whistle". After that, it operates normally.

I have another L8400P, and it switches on silently. As do two other JBL subs (E150P, Sub 12). Currently, only the "noisy" sub is hooked up to the system, which is a 7.1, consisting of all Studio L Series speakers.

Any suggestions as to the cause of this "whistle"?

I seem to recall reading a service bulletin on this very subject from JBL, but darned if I can find it after searching the net...

Any advice would be appreciated.