Hmmm ... now where did I read this before? (hint look earlier in this post ;-)Does it go away when you insert a floppy? Larry Pina says this can be because of a particular model of 800K floppy drive and is insignificant. He also mentions a "time-bomb"...
As for the ticking in the power supply, oh yeah baby! Tkae a look at Tom Lee's MacPlus paper online as well as the Pina book if you have it ... if not get it!