Speaker Oscillation issue ?

@tommypenngotti  It may be that the failing equipment needs a signal to push it over the edge. Sitting with no signal it might seem just fine.

@atmasphere 

was thinking I can disconnect preamp & just turn on amp...should get that oscillation/motorboat issue w/o music right? If nothing happens plug in preamp & try same method to isolate what's causing it? thanks ! 

Pay heed to Ralph, a wise man.

This is clearly an electronics issue.

It will be either the amp or preamp. disconnect the preamp from the amp and see if the problem goes away.

If yes=> preamp needs service

If no=> amplifier needs service

This kind of oscillation (called 'motorboating') can be caused by failing filter capacitors in the power supply. This type of failure can lead to failure of the power transformer in that unit, so its a good idea to get a handle on this and find out what is going on. Its really a bummer to have a power transformer fail.

I'd use a multimeter and disconnect your speaker, just in case. :)

Disconnect all your inputs and see if the problem goes away.