With my old Tacoma, I did A TON of power steering diagnosis and repair... Damn I hated that.
First, check your fluid level.
Then if that's fine, I would flush the system. I had that down to a science...
I like to buy 2 bottles of ATF (NOT POWER STEERING FLUID.....ATF!!). One is for flushing, and the other is for filling. Place a large cup on the frame rail to the left of the pump. Pull the low pressure return line (the one with a regular hose clamp and rubber hose) off of the reservoir. Try to catch as much of the fluid as you can into the cup, then route the return hose inside of it. Now, pull each of the wires off the ignition coils on the passenger side to disable the ignition (but make sure you keep track of which goes where). This is to keep the return pressure manageable. If you just start the engine, you're asking for a HUGE mess... At this point, have a friend sit in the driver's seat to crank the engine and turn the wheels lock to lock while you pour ATF slowly into the reservoir. Keep flushing until you only see clean red ATF coming out steadily. Put the return line back on, and the wires back on to the coils. Now fill up the reservoir. Start then engine, and turn the wheel lock to lock several times. You should see the fluid level subsiding with each turn, so keep topping it off periodically. Hopefully as you continue to do this it will get quieter and easier to turn the wheels.
