SOunds like the power supply voltage is fluctuating with load, as in floppy running or not. Caps are likely culprits, and the whistle may be from the flyback. Most usual problem there is cracked solder due to heat cycling. Reflow the solder on all the transformer joints and other hot parts in any case. If you don't run the machine with loose flyback connections, the transformer will last just about forever. Horizontal retrace lines on the screen may be due to the internal brightness control turned up too far. Proper setting is to turn the user brightness all the way up, then set the internal control just below the point where retrace is visible (or in some Macs where focus goes to heck). Retrace lines could also be due to voltage setting being off, so a voltmeter check is in order. Good luck, and learn to solder. It's a very useful skill.