static/electrical interference sounds from speaker

Ground loop or more likely failed component.

Check you have a proper ground (no cheater plugs)and try plugging everything into the same recepticle (OPPO 983 and Amp) - use a power bar if necessary. If that does not cure it then one of the power supply caps or a transistor may be on its last legs (works cool but fails under stress/heat). (Some type of caps will arc as they fail and may self repair but if it is dried out or seriously damaged then you'll need to raplace it)

Another way to avoid/minimize ground loops is to use TOSLINK from source to amp or XLR rather than RCA type analog connections...

it's just process of elimination. You'll be unplugging interconnects, powercords, and speaker cables to see what's the offending cause. Once you find it, you can issolate it.
Are your speaker cables touching anything with power? Are they in the wall or on the floor (possibly touching some other gear?
Otherwise, yes, try disconnecting sources, one at a time (including interconnnects), and see if the noise goes away.
(also, there is no reason you can't use the cheater-plugs on some of your pieces, as long at you have at least one or two of your components in your system grounded safetly - as they'll all be connected anyway, and thus grounded.

If I'm wrong on the "grounded anyway" thing, someone who's an electrical expert PLEASE ADVISE othewise!
No-one wants to get electricuted here, I'm sure.

Funny, while I'm looking at this post, I noticed my little computer speakers were making the same noises - lots of crackling and static sounding. I moved some wires off the speaker wires and power cord, and the noises are all gone. It's the same kinda stuff. You'll have to move things and trouble-shoot