My timing belt squeals just for a second when I start it (slightly loose). I had it loosen 6 months ago because it was whining (tight). Well I think I need to get it a snag tighter. I watched the mechanic when he loosen it.. (5 minutes) Seems like he was just turning some bolt...but not sure which?

In the diagram is "A" the nut bolt which I adjust? Can that be access w/o taking off the plastic cover?

 

First, before saying how, I'll say that the timing belt probably isn't squealing. It's a toothed belt, they don't do that. It's more likely one of the external drive belts (alternator, PS). Or maybe it's the tensioner pulley bearing?

"A" is the big crankshaft pulley. You won't easily loosen that one.
"B" is the adjuster. It's spring-loaded, & you adjust it this way...

Take all the spark plugs out so it's easier to spin the engine. Turn the crankshaft pulley counterclockwise, the direction the engine runs, for a few revolutions. With the spark plugs removed, it won't want to turn back when you stop.

Loosen the bolt "B" by only 1/8 or 1/4 turn. Turn the crankshaft counterclockwise just a bit. This should only be enough to make the long span from A to D tight, & allow the slack to move over to the other side. The spring-loaded tensioner B will take up the slack. Don't let go of the crank pulley, don't allow it to back up at all. While holding the crank pulley, tighten the tensioner bolt to lock the tensioner into position.

Incidentally, "C" is the waterpump in case you're wondering.

 

Yes definitely would not be a timing belt "slipping".