When I change volume on my Marantz 18EX, both by rotating the knob and by using the remote (which does not rotate the knob), I hear audible pretty high-pitch clicks in the speakers. They stop when I stop changing the volume. Most noticable when I change volume fast. Is this something known about these receivers? Have other owners noticed it? Should I be worried about this? In general, I read some threads about problems people were having with Marantz receivers (slow digital audio format pickup, video sync problems).. was there any "resolution", fix from marantz, or did they fix it in newer-run production units? How do I tell when my unit was produced? It's only got a random cryptic number on its back... Thanks!